Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

152 files changed, 8494 insertions, 0 deletions

diff --git a/testing/web-platform/tests/dom/events/AddEventListenerOptions-once.any.js b/testing/web-platform/tests/dom/events/AddEventListenerOptions-once.any.js
new file mode 100644
index 0000000000..b4edd4345c
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/AddEventListenerOptions-once.any.js
@@ -0,0 +1,96 @@
+// META: title=AddEventListenerOptions.once
+
+"use strict";
+
+test(function() {
+  var invoked_once = false;
+  var invoked_normal = false;
+  function handler_once() {
+    invoked_once = true;
+  }
+  function handler_normal() {
+    invoked_normal = true;
+  }
+
+  const et = new EventTarget();
+  et.addEventListener('test', handler_once, {once: true});
+  et.addEventListener('test', handler_normal);
+  et.dispatchEvent(new Event('test'));
+  assert_equals(invoked_once, true, "Once handler should be invoked");
+  assert_equals(invoked_normal, true, "Normal handler should be invoked");
+
+  invoked_once = false;
+  invoked_normal = false;
+  et.dispatchEvent(new Event('test'));
+  assert_equals(invoked_once, false, "Once handler shouldn't be invoked again");
+  assert_equals(invoked_normal, true, "Normal handler should be invoked again");
+  et.removeEventListener('test', handler_normal);
+}, "Once listener should be invoked only once");
+
+test(function() {
+  const et = new EventTarget();
+  var invoked_count = 0;
+  function handler() {
+    invoked_count++;
+    if (invoked_count == 1)
+    et.dispatchEvent(new Event('test'));
+  }
+  et.addEventListener('test', handler, {once: true});
+  et.dispatchEvent(new Event('test'));
+  assert_equals(invoked_count, 1, "Once handler should only be invoked once");
+
+  invoked_count = 0;
+  function handler2() {
+    invoked_count++;
+    if (invoked_count == 1)
+      et.addEventListener('test', handler2, {once: true});
+    if (invoked_count <= 2)
+      et.dispatchEvent(new Event('test'));
+  }
+  et.addEventListener('test', handler2, {once: true});
+  et.dispatchEvent(new Event('test'));
+  assert_equals(invoked_count, 2, "Once handler should only be invoked once after each adding");
+}, "Once listener should be invoked only once even if the event is nested");
+
+test(function() {
+  var invoked_count = 0;
+  function handler() {
+    invoked_count++;
+  }
+
+  const et = new EventTarget();
+
+  et.addEventListener('test', handler, {once: true});
+  et.addEventListener('test', handler);
+  et.dispatchEvent(new Event('test'));
+  assert_equals(invoked_count, 1, "The handler should only be added once");
+
+  invoked_count = 0;
+  et.dispatchEvent(new Event('test'));
+  assert_equals(invoked_count, 0, "The handler was added as a once listener");
+
+  invoked_count = 0;
+  et.addEventListener('test', handler, {once: true});
+  et.removeEventListener('test', handler);
+  et.dispatchEvent(new Event('test'));
+  assert_equals(invoked_count, 0, "The handler should have been removed");
+}, "Once listener should be added / removed like normal listeners");
+
+test(function() {
+  const et = new EventTarget();
+
+  var invoked_count = 0;
+
+  for (let n = 4; n > 0; n--) {
+    et.addEventListener('test', (e) => {
+      invoked_count++;
+      e.stopImmediatePropagation();
+    }, {once: true});
+  }
+
+  for (let n = 4; n > 0; n--) {
+    et.dispatchEvent(new Event('test'));
+  }
+
+  assert_equals(invoked_count, 4, "The listeners should be invoked");
+}, "Multiple once listeners should be invoked even if the stopImmediatePropagation is set");
diff --git a/testing/web-platform/tests/dom/events/AddEventListenerOptions-passive.any.js b/testing/web-platform/tests/dom/events/AddEventListenerOptions-passive.any.js
new file mode 100644
index 0000000000..8e59cf5b37
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/AddEventListenerOptions-passive.any.js
@@ -0,0 +1,134 @@
+// META: title=AddEventListenerOptions.passive
+
+test(function() {
+  var supportsPassive = false;
+  var query_options = {
+    get passive() {
+      supportsPassive = true;
+      return false;
+    },
+    get dummy() {
+      assert_unreached("dummy value getter invoked");
+      return false;
+    }
+  };
+
+  const et = new EventTarget();
+  et.addEventListener('test_event', null, query_options);
+  assert_true(supportsPassive, "addEventListener doesn't support the passive option");
+
+  supportsPassive = false;
+  et.removeEventListener('test_event', null, query_options);
+  assert_false(supportsPassive, "removeEventListener supports the passive option when it should not");
+}, "Supports passive option on addEventListener only");
+
+function testPassiveValue(optionsValue, expectedDefaultPrevented, existingEventTarget) {
+  var defaultPrevented = undefined;
+  var handler = function handler(e) {
+    assert_false(e.defaultPrevented, "Event prematurely marked defaultPrevented");
+    e.preventDefault();
+    defaultPrevented = e.defaultPrevented;
+  }
+  const et = existingEventTarget || new EventTarget();
+  et.addEventListener('test', handler, optionsValue);
+  var uncanceled = et.dispatchEvent(new Event('test', {bubbles: true, cancelable: true}));
+
+  assert_equals(defaultPrevented, expectedDefaultPrevented, "Incorrect defaultPrevented for options: " + JSON.stringify(optionsValue));
+  assert_equals(uncanceled, !expectedDefaultPrevented, "Incorrect return value from dispatchEvent");
+
+  et.removeEventListener('test', handler, optionsValue);
+}
+
+test(function() {
+  testPassiveValue(undefined, true);
+  testPassiveValue({}, true);
+  testPassiveValue({passive: false}, true);
+  testPassiveValue({passive: true}, false);
+  testPassiveValue({passive: 0}, true);
+  testPassiveValue({passive: 1}, false);
+}, "preventDefault should be ignored if-and-only-if the passive option is true");
+
+function testPassiveValueOnReturnValue(test, optionsValue, expectedDefaultPrevented) {
+  var defaultPrevented = undefined;
+  var handler = test.step_func(e => {
+    assert_false(e.defaultPrevented, "Event prematurely marked defaultPrevented");
+    e.returnValue = false;
+    defaultPrevented = e.defaultPrevented;
+  });
+  const et = new EventTarget();
+  et.addEventListener('test', handler, optionsValue);
+  var uncanceled = et.dispatchEvent(new Event('test', {bubbles: true, cancelable: true}));
+
+  assert_equals(defaultPrevented, expectedDefaultPrevented, "Incorrect defaultPrevented for options: " + JSON.stringify(optionsValue));
+  assert_equals(uncanceled, !expectedDefaultPrevented, "Incorrect return value from dispatchEvent");
+
+  et.removeEventListener('test', handler, optionsValue);
+}
+
+async_test(t => {
+  testPassiveValueOnReturnValue(t, undefined, true);
+  testPassiveValueOnReturnValue(t, {}, true);
+  testPassiveValueOnReturnValue(t, {passive: false}, true);
+  testPassiveValueOnReturnValue(t, {passive: true}, false);
+  testPassiveValueOnReturnValue(t, {passive: 0}, true);
+  testPassiveValueOnReturnValue(t, {passive: 1}, false);
+  t.done();
+}, "returnValue should be ignored if-and-only-if the passive option is true");
+
+function testPassiveWithOtherHandlers(optionsValue, expectedDefaultPrevented) {
+  var handlerInvoked1 = false;
+  var dummyHandler1 = function() {
+    handlerInvoked1 = true;
+  };
+  var handlerInvoked2 = false;
+  var dummyHandler2 = function() {
+    handlerInvoked2 = true;
+  };
+
+  const et = new EventTarget();
+  et.addEventListener('test', dummyHandler1, {passive:true});
+  et.addEventListener('test', dummyHandler2);
+
+  testPassiveValue(optionsValue, expectedDefaultPrevented, et);
+
+  assert_true(handlerInvoked1, "Extra passive handler not invoked");
+  assert_true(handlerInvoked2, "Extra non-passive handler not invoked");
+
+  et.removeEventListener('test', dummyHandler1);
+  et.removeEventListener('test', dummyHandler2);
+}
+
+test(function() {
+  testPassiveWithOtherHandlers({}, true);
+  testPassiveWithOtherHandlers({passive: false}, true);
+  testPassiveWithOtherHandlers({passive: true}, false);
+}, "passive behavior of one listener should be unaffected by the presence of other listeners");
+
+function testOptionEquivalence(optionValue1, optionValue2, expectedEquality) {
+  var invocationCount = 0;
+  var handler = function handler(e) {
+    invocationCount++;
+  }
+  const et = new EventTarget();
+  et.addEventListener('test', handler, optionValue1);
+  et.addEventListener('test', handler, optionValue2);
+  et.dispatchEvent(new Event('test', {bubbles: true}));
+  assert_equals(invocationCount, expectedEquality ? 1 : 2, "equivalence of options " +
+    JSON.stringify(optionValue1) + " and " + JSON.stringify(optionValue2));
+  et.removeEventListener('test', handler, optionValue1);
+  et.removeEventListener('test', handler, optionValue2);
+}
+
+test(function() {
+  // Sanity check options that should be treated as distinct handlers
+  testOptionEquivalence({capture:true}, {capture:false, passive:false}, false);
+  testOptionEquivalence({capture:true}, {passive:true}, false);
+
+  // Option values that should be treated as equivalent
+  testOptionEquivalence({}, {passive:false}, true);
+  testOptionEquivalence({passive:true}, {passive:false}, true);
+  testOptionEquivalence(undefined, {passive:true}, true);
+  testOptionEquivalence({capture: true, passive: false}, {capture: true, passive: true}, true);
+
+}, "Equivalence of option values");
+
diff --git a/testing/web-platform/tests/dom/events/AddEventListenerOptions-signal.any.js b/testing/web-platform/tests/dom/events/AddEventListenerOptions-signal.any.js
new file mode 100644
index 0000000000..e6a3426159
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/AddEventListenerOptions-signal.any.js
@@ -0,0 +1,143 @@
+'use strict';
+
+test(function() {
+  let count = 0;
+  function handler() {
+    count++;
+  }
+  const et = new EventTarget();
+  const controller = new AbortController();
+  et.addEventListener('test', handler, { signal: controller.signal });
+  et.dispatchEvent(new Event('test'));
+  assert_equals(count, 1, "Adding a signal still adds a listener");
+  et.dispatchEvent(new Event('test'));
+  assert_equals(count, 2, "The listener was not added with the once flag");
+  controller.abort();
+  et.dispatchEvent(new Event('test'));
+  assert_equals(count, 2, "Aborting on the controller removes the listener");
+  et.addEventListener('test', handler, { signal: controller.signal });
+  et.dispatchEvent(new Event('test'));
+  assert_equals(count, 2, "Passing an aborted signal never adds the handler");
+}, "Passing an AbortSignal to addEventListener options should allow removing a listener");
+
+test(function() {
+  let count = 0;
+  function handler() {
+    count++;
+  }
+  const et = new EventTarget();
+  const controller = new AbortController();
+  et.addEventListener('test', handler, { signal: controller.signal });
+  et.removeEventListener('test', handler);
+  et.dispatchEvent(new Event('test'));
+  assert_equals(count, 0, "The listener was still removed");
+}, "Passing an AbortSignal to addEventListener does not prevent removeEventListener");
+
+test(function() {
+  let count = 0;
+  function handler() {
+    count++;
+  }
+  const et = new EventTarget();
+  const controller = new AbortController();
+  et.addEventListener('test', handler, { signal: controller.signal, once: true });
+  controller.abort();
+  et.dispatchEvent(new Event('test'));
+  assert_equals(count, 0, "The listener was still removed");
+}, "Passing an AbortSignal to addEventListener works with the once flag");
+
+test(function() {
+  let count = 0;
+  function handler() {
+    count++;
+  }
+  const et = new EventTarget();
+  const controller = new AbortController();
+  et.addEventListener('test', handler, { signal: controller.signal, once: true });
+  et.removeEventListener('test', handler);
+  et.dispatchEvent(new Event('test'));
+  assert_equals(count, 0, "The listener was still removed");
+}, "Removing a once listener works with a passed signal");
+
+test(function() {
+  let count = 0;
+  function handler() {
+    count++;
+  }
+  const et = new EventTarget();
+  const controller = new AbortController();
+  et.addEventListener('first', handler, { signal: controller.signal, once: true });
+  et.addEventListener('second', handler, { signal: controller.signal, once: true });
+  controller.abort();
+  et.dispatchEvent(new Event('first'));
+  et.dispatchEvent(new Event('second'));
+  assert_equals(count, 0, "The listener was still removed");
+}, "Passing an AbortSignal to multiple listeners");
+
+test(function() {
+  let count = 0;
+  function handler() {
+    count++;
+  }
+  const et = new EventTarget();
+  const controller = new AbortController();
+  et.addEventListener('test', handler, { signal: controller.signal, capture: true });
+  controller.abort();
+  et.dispatchEvent(new Event('test'));
+  assert_equals(count, 0, "The listener was still removed");
+}, "Passing an AbortSignal to addEventListener works with the capture flag");
+
+test(function() {
+  let count = 0;
+  function handler() {
+    count++;
+  }
+  const et = new EventTarget();
+  const controller = new AbortController();
+  et.addEventListener('test', () => {
+    controller.abort();
+  }, { signal: controller.signal });
+  et.addEventListener('test', handler, { signal: controller.signal });
+  et.dispatchEvent(new Event('test'));
+  assert_equals(count, 0, "The listener was still removed");
+}, "Aborting from a listener does not call future listeners");
+
+test(function() {
+  let count = 0;
+  function handler() {
+    count++;
+  }
+  const et = new EventTarget();
+  const controller = new AbortController();
+  et.addEventListener('test', () => {
+    et.addEventListener('test', handler, { signal: controller.signal });
+    controller.abort();
+  }, { signal: controller.signal });
+  et.dispatchEvent(new Event('test'));
+  assert_equals(count, 0, "The listener was still removed");
+}, "Adding then aborting a listener in another listener does not call it");
+
+test(function() {
+  const et = new EventTarget();
+  const ac = new AbortController();
+  let count = 0;
+  et.addEventListener('foo', () => {
+    et.addEventListener('foo', () => {
+      count++;
+      if (count > 5) ac.abort();
+      et.dispatchEvent(new Event('foo'));
+    }, { signal: ac.signal });
+    et.dispatchEvent(new Event('foo'));
+  }, { once: true });
+  et.dispatchEvent(new Event('foo'));
+}, "Aborting from a nested listener should remove it");
+
+test(function() {
+  const et = new EventTarget();
+  assert_throws_js(TypeError, () => { et.addEventListener("foo", () => {}, { signal: null }); });
+}, "Passing null as the signal should throw");
+
+test(function() {
+  const et = new EventTarget();
+  assert_throws_js(TypeError, () => { et.addEventListener("foo", null, { signal: null }); });
+}, "Passing null as the signal should throw (listener is also null)");
diff --git a/testing/web-platform/tests/dom/events/Body-FrameSet-Event-Handlers.html b/testing/web-platform/tests/dom/events/Body-FrameSet-Event-Handlers.html
new file mode 100644
index 0000000000..3a891158d5
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Body-FrameSet-Event-Handlers.html
@@ -0,0 +1,123 @@
+<!DOCTYPE html>
+<html>
+<title>HTMLBodyElement and HTMLFrameSetElement Event Handler Tests</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<script>
+function getObject(interface) {
+    switch(interface) {
+        case "Element":
+            var e = document.createElementNS("http://example.com/", "example");
+            assert_true(e instanceof Element);
+            assert_false(e instanceof HTMLElement);
+            assert_false(e instanceof SVGElement);
+            return e;
+        case "HTMLElement":
+            var e = document.createElement("html");
+            assert_true(e instanceof HTMLElement);
+            return e;
+        case "HTMLBodyElement":
+            var e = document.createElement("body");
+            assert_true(e instanceof HTMLBodyElement);
+            return e;
+        case "HTMLFormElement":
+            var e = document.createElement("form");
+            assert_true(e instanceof HTMLFormElement);
+            return e;
+        case "HTMLFrameSetElement":
+            var e = document.createElement("frameset");
+            assert_true(e instanceof HTMLFrameSetElement);
+            return e;
+        case "SVGElement":
+            var e = document.createElementNS("http://www.w3.org/2000/svg", "rect");
+            assert_true(e instanceof SVGElement);
+            return e;
+        case "Document":
+            assert_true(document instanceof Document);
+            return document;
+        case "Window":
+            assert_true(window instanceof Window);
+            return window;
+    }
+    assert_unreached();
+}
+
+function testSet(interface, attribute) {
+    test(function() {
+        var object = getObject(interface);
+        function nop() {}
+        assert_equals(object[attribute], null, "Initially null");
+        object[attribute] = nop;
+        assert_equals(object[attribute], nop, "Return same function");
+        object[attribute] = "";
+        assert_equals(object[attribute], null, "Return null after setting string");
+        object[attribute] = null;
+        assert_equals(object[attribute], null, "Finally null");
+    }, "Set " + interface + "." + attribute);
+}
+
+function testReflect(interface, attribute) {
+    test(function() {
+        var element = getObject(interface);
+        assert_false(element.hasAttribute(attribute), "Initially missing");
+        element.setAttribute(attribute, "return");
+        assert_equals(element.getAttribute(attribute), "return", "Return same string");
+        assert_equals(typeof element[attribute], "function", "Convert to function");
+        element.removeAttribute(attribute);
+    }, "Reflect " + interface + "." + attribute);
+}
+
+function testForwardToWindow(interface, attribute) {
+    test(function() {
+        var element = getObject(interface);
+        window[attribute] = null;
+        element.setAttribute(attribute, "return");
+        assert_equals(typeof window[attribute], "function", "Convert to function");
+        assert_equals(window[attribute], element[attribute], "Forward content attribute");
+        function nop() {}
+        element[attribute] = nop;
+        assert_equals(window[attribute], nop, "Forward IDL attribute");
+        window[attribute] = null;
+    }, "Forward " + interface + "." + attribute + " to Window");
+}
+
+// Object.propertyIsEnumerable cannot be used because it doesn't
+// work with properties inherited through the prototype chain.
+function getEnumerable(interface) {
+    var enumerable = {};
+    for (var attribute in getObject(interface)) {
+        enumerable[attribute] = true;
+    }
+    return enumerable;
+}
+
+var enumerableCache = {};
+function testEnumerate(interface, attribute) {
+    if (!(interface in enumerableCache)) {
+        enumerableCache[interface] = getEnumerable(interface);
+    }
+    test(function() {
+        assert_true(enumerableCache[interface][attribute]);
+    }, "Enumerate " + interface + "." + attribute);
+}
+
+[
+    "onblur",
+    "onerror",
+    "onfocus",
+    "onload",
+    "onscroll",
+    "onresize"
+].forEach(function(attribute) {
+    testSet("HTMLBodyElement", attribute);
+    testEnumerate("HTMLBodyElement", attribute);
+    testReflect("HTMLBodyElement", attribute);
+    testForwardToWindow("HTMLBodyElement", attribute);
+    testSet("HTMLFrameSetElement", attribute);
+    testEnumerate("HTMLFrameSetElement", attribute);
+    testReflect("HTMLFrameSetElement", attribute);
+    testForwardToWindow("HTMLFrameSetElement", attribute);
+});
+</script>
+</html>
diff --git a/testing/web-platform/tests/dom/events/CustomEvent.html b/testing/web-platform/tests/dom/events/CustomEvent.html
new file mode 100644
index 0000000000..87050943f9
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/CustomEvent.html
@@ -0,0 +1,35 @@
+<!doctype html>
+<title>CustomEvent</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+test(function() {
+  var type = "foo";
+
+  var target = document.createElement("div");
+  target.addEventListener(type, this.step_func(function(evt) {
+    assert_equals(evt.type, type);
+  }), true);
+
+  var fooEvent = document.createEvent("CustomEvent");
+  fooEvent.initEvent(type, true, true);
+  target.dispatchEvent(fooEvent);
+}, "CustomEvent dispatching.");
+
+test(function() {
+    var e = document.createEvent("CustomEvent");
+    assert_throws_js(TypeError, function() {
+        e.initCustomEvent();
+    });
+}, "First parameter to initCustomEvent should be mandatory.");
+
+test(function() {
+    var e = document.createEvent("CustomEvent");
+    e.initCustomEvent("foo");
+    assert_equals(e.type, "foo", "type");
+    assert_false(e.bubbles, "bubbles");
+    assert_false(e.cancelable, "cancelable");
+    assert_equals(e.detail, null, "detail");
+}, "initCustomEvent's default parameter values.");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-cancelBubble.html b/testing/web-platform/tests/dom/events/Event-cancelBubble.html
new file mode 100644
index 0000000000..d8d2d7239d
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-cancelBubble.html
@@ -0,0 +1,132 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Event.cancelBubble</title>
+  <link rel="author" title="Chris Rebert" href="http://chrisrebert.com">
+  <link rel="help" href="https://dom.spec.whatwg.org/#dom-event-cancelbubble">
+  <meta name="flags" content="dom">
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+  <div id="outer">
+    <div id="middle">
+      <div id="inner"></div>
+    </div>
+  </div>
+  <script>
+test(function () {
+  // See https://dom.spec.whatwg.org/#stop-propagation-flag
+  var e = document.createEvent('Event');
+  assert_false(e.cancelBubble, "cancelBubble must be false after event creation.");
+}, "cancelBubble must be false when an event is initially created.");
+
+test(function () {
+  // See https://dom.spec.whatwg.org/#concept-event-initialize
+
+  // Event which bubbles.
+  var one = document.createEvent('Event');
+  one.cancelBubble = true;
+  one.initEvent('foo', true/*bubbles*/, false/*cancelable*/);
+  assert_false(one.cancelBubble, "initEvent() must set cancelBubble to false. [bubbles=true]");
+  // Re-initialization.
+  one.cancelBubble = true;
+  one.initEvent('foo', true/*bubbles*/, false/*cancelable*/);
+  assert_false(one.cancelBubble, "2nd initEvent() call must set cancelBubble to false. [bubbles=true]");
+
+  // Event which doesn't bubble.
+  var two = document.createEvent('Event');
+  two.cancelBubble = true;
+  two.initEvent('foo', false/*bubbles*/, false/*cancelable*/);
+  assert_false(two.cancelBubble, "initEvent() must set cancelBubble to false. [bubbles=false]");
+  // Re-initialization.
+  two.cancelBubble = true;
+  two.initEvent('foo', false/*bubbles*/, false/*cancelable*/);
+  assert_false(two.cancelBubble, "2nd initEvent() call must set cancelBubble to false. [bubbles=false]");
+}, "Initializing an event must set cancelBubble to false.");
+
+test(function () {
+  // See https://dom.spec.whatwg.org/#dom-event-stoppropagation
+  var e = document.createEvent('Event');
+  e.stopPropagation();
+  assert_true(e.cancelBubble, "stopPropagation() must set cancelBubble to true.");
+}, "stopPropagation() must set cancelBubble to true.");
+
+test(function () {
+  // See https://dom.spec.whatwg.org/#dom-event-stopimmediatepropagation
+  var e = document.createEvent('Event');
+  e.stopImmediatePropagation();
+  assert_true(e.cancelBubble, "stopImmediatePropagation() must set cancelBubble to true.");
+}, "stopImmediatePropagation() must set cancelBubble to true.");
+
+test(function () {
+  var one = document.createEvent('Event');
+  one.stopPropagation();
+  one.cancelBubble = false;
+  assert_true(one.cancelBubble, "cancelBubble must still be true after attempting to set it to false.");
+}, "Event.cancelBubble=false must have no effect.");
+
+test(function (t) {
+  var outer = document.getElementById('outer');
+  var middle = document.getElementById('middle');
+  var inner = document.getElementById('inner');
+
+  outer.addEventListener('barbaz', t.step_func(function () {
+    assert_unreached("Setting Event.cancelBubble=false after setting Event.cancelBubble=true should have no effect.");
+  }), false/*useCapture*/);
+
+  middle.addEventListener('barbaz', function (e) {
+    e.cancelBubble = true;// Stop propagation.
+    e.cancelBubble = false;// Should be a no-op.
+  }, false/*useCapture*/);
+
+  var barbazEvent = document.createEvent('Event');
+  barbazEvent.initEvent('barbaz', true/*bubbles*/, false/*cancelable*/);
+  inner.dispatchEvent(barbazEvent);
+}, "Event.cancelBubble=false must have no effect during event propagation.");
+
+test(function () {
+  // See https://dom.spec.whatwg.org/#concept-event-dispatch
+  // "14. Unset event’s [...] stop propagation flag,"
+  var e = document.createEvent('Event');
+  e.initEvent('foobar', true/*bubbles*/, true/*cancelable*/);
+  document.body.addEventListener('foobar', function listener(e) {
+    e.stopPropagation();
+  });
+  document.body.dispatchEvent(e);
+  assert_false(e.cancelBubble, "cancelBubble must be false after an event has been dispatched.");
+}, "cancelBubble must be false after an event has been dispatched.");
+
+test(function (t) {
+  var outer = document.getElementById('outer');
+  var middle = document.getElementById('middle');
+  var inner = document.getElementById('inner');
+
+  var propagationStopper = function (e) {
+    e.cancelBubble = true;
+  };
+
+  // Bubble phase
+  middle.addEventListener('bar', propagationStopper, false/*useCapture*/);
+  outer.addEventListener('bar', t.step_func(function listenerOne() {
+    assert_unreached("Setting cancelBubble=true should stop the event from bubbling further.");
+  }), false/*useCapture*/);
+
+  var barEvent = document.createEvent('Event');
+  barEvent.initEvent('bar', true/*bubbles*/, false/*cancelable*/);
+  inner.dispatchEvent(barEvent);
+
+  // Capture phase
+  outer.addEventListener('qux', propagationStopper, true/*useCapture*/);
+  middle.addEventListener('qux', t.step_func(function listenerTwo() {
+    assert_unreached("Setting cancelBubble=true should stop the event from propagating further, including during the Capture Phase.");
+  }), true/*useCapture*/);
+
+  var quxEvent = document.createEvent('Event');
+  quxEvent.initEvent('qux', false/*bubbles*/, false/*cancelable*/);
+  inner.dispatchEvent(quxEvent);
+}, "Event.cancelBubble=true must set the stop propagation flag.");
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/dom/events/Event-constants.html b/testing/web-platform/tests/dom/events/Event-constants.html
new file mode 100644
index 0000000000..635e9894d9
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-constants.html
@@ -0,0 +1,23 @@
+<!doctype html>
+<title>Event constants</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../constants.js"></script>
+<div id="log"></div>
+<script>
+var objects;
+setup(function() {
+  objects = [
+    [Event, "Event interface object"],
+    [Event.prototype, "Event prototype object"],
+    [document.createEvent("Event"), "Event object"],
+    [document.createEvent("CustomEvent"), "CustomEvent object"]
+  ]
+})
+testConstants(objects, [
+  ["NONE", 0],
+  ["CAPTURING_PHASE", 1],
+  ["AT_TARGET", 2],
+  ["BUBBLING_PHASE", 3]
+], "eventPhase")
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-constructors.any.js b/testing/web-platform/tests/dom/events/Event-constructors.any.js
new file mode 100644
index 0000000000..faa623ea92
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-constructors.any.js
@@ -0,0 +1,120 @@
+// META: title=Event constructors
+
+test(function() {
+  assert_throws_js(
+    TypeError,
+    () => Event(""),
+    "Calling Event constructor without 'new' must throw")
+})
+test(function() {
+  assert_throws_js(TypeError, function() {
+    new Event()
+  })
+})
+test(function() {
+  var test_error = { name: "test" }
+  assert_throws_exactly(test_error, function() {
+    new Event({ toString: function() { throw test_error; } })
+  })
+})
+test(function() {
+  var ev = new Event("")
+  assert_equals(ev.type, "")
+  assert_equals(ev.target, null)
+  assert_equals(ev.srcElement, null)
+  assert_equals(ev.currentTarget, null)
+  assert_equals(ev.eventPhase, Event.NONE)
+  assert_equals(ev.bubbles, false)
+  assert_equals(ev.cancelable, false)
+  assert_equals(ev.defaultPrevented, false)
+  assert_equals(ev.returnValue, true)
+  assert_equals(ev.isTrusted, false)
+  assert_true(ev.timeStamp > 0)
+  assert_true("initEvent" in ev)
+})
+test(function() {
+  var ev = new Event("test")
+  assert_equals(ev.type, "test")
+  assert_equals(ev.target, null)
+  assert_equals(ev.srcElement, null)
+  assert_equals(ev.currentTarget, null)
+  assert_equals(ev.eventPhase, Event.NONE)
+  assert_equals(ev.bubbles, false)
+  assert_equals(ev.cancelable, false)
+  assert_equals(ev.defaultPrevented, false)
+  assert_equals(ev.returnValue, true)
+  assert_equals(ev.isTrusted, false)
+  assert_true(ev.timeStamp > 0)
+  assert_true("initEvent" in ev)
+})
+test(function() {
+  assert_throws_js(TypeError, function() { Event("test") },
+                   'Calling Event constructor without "new" must throw');
+})
+test(function() {
+  var ev = new Event("I am an event", { bubbles: true, cancelable: false})
+  assert_equals(ev.type, "I am an event")
+  assert_equals(ev.bubbles, true)
+  assert_equals(ev.cancelable, false)
+})
+test(function() {
+  var ev = new Event("@", { bubblesIGNORED: true, cancelable: true})
+  assert_equals(ev.type, "@")
+  assert_equals(ev.bubbles, false)
+  assert_equals(ev.cancelable, true)
+})
+test(function() {
+  var ev = new Event("@", { "bubbles\0IGNORED": true, cancelable: true})
+  assert_equals(ev.type, "@")
+  assert_equals(ev.bubbles, false)
+  assert_equals(ev.cancelable, true)
+})
+test(function() {
+  var ev = new Event("Xx", { cancelable: true})
+  assert_equals(ev.type, "Xx")
+  assert_equals(ev.bubbles, false)
+  assert_equals(ev.cancelable, true)
+})
+test(function() {
+  var ev = new Event("Xx", {})
+  assert_equals(ev.type, "Xx")
+  assert_equals(ev.bubbles, false)
+  assert_equals(ev.cancelable, false)
+})
+test(function() {
+  var ev = new Event("Xx", {bubbles: true, cancelable: false, sweet: "x"})
+  assert_equals(ev.type, "Xx")
+  assert_equals(ev.bubbles, true)
+  assert_equals(ev.cancelable, false)
+  assert_equals(ev.sweet, undefined)
+})
+test(function() {
+  var called = []
+  var ev = new Event("Xx", {
+    get cancelable() {
+      called.push("cancelable")
+      return false
+    },
+    get bubbles() {
+      called.push("bubbles")
+      return true;
+    },
+    get sweet() {
+      called.push("sweet")
+      return "x"
+    }
+  })
+  assert_array_equals(called, ["bubbles", "cancelable"])
+  assert_equals(ev.type, "Xx")
+  assert_equals(ev.bubbles, true)
+  assert_equals(ev.cancelable, false)
+  assert_equals(ev.sweet, undefined)
+})
+test(function() {
+  var ev = new CustomEvent("$", {detail: 54, sweet: "x", sweet2: "x", cancelable:true})
+  assert_equals(ev.type, "$")
+  assert_equals(ev.bubbles, false)
+  assert_equals(ev.cancelable, true)
+  assert_equals(ev.sweet, undefined)
+  assert_equals(ev.detail, 54)
+})
diff --git a/testing/web-platform/tests/dom/events/Event-defaultPrevented-after-dispatch.html b/testing/web-platform/tests/dom/events/Event-defaultPrevented-after-dispatch.html
new file mode 100644
index 0000000000..8fef005eb5
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-defaultPrevented-after-dispatch.html
@@ -0,0 +1,44 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Event.defaultPrevented is not reset after dispatchEvent()</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+<div id=log></div>
+<input id="target" type="hidden" value=""/>
+<script>
+test(function() {
+    var EVENT = "foo";
+    var TARGET = document.getElementById("target");
+    var evt = document.createEvent("Event");
+    evt.initEvent(EVENT, true, true);
+
+    TARGET.addEventListener(EVENT, this.step_func(function(e) {
+        e.preventDefault();
+        assert_true(e.defaultPrevented, "during dispatch");
+    }), true);
+    TARGET.dispatchEvent(evt);
+
+    assert_true(evt.defaultPrevented, "after dispatch");
+    assert_equals(evt.target, TARGET);
+    assert_equals(evt.srcElement, TARGET);
+}, "Default prevention via preventDefault");
+
+test(function() {
+    var EVENT = "foo";
+    var TARGET = document.getElementById("target");
+    var evt = document.createEvent("Event");
+    evt.initEvent(EVENT, true, true);
+
+    TARGET.addEventListener(EVENT, this.step_func(function(e) {
+        e.returnValue = false;
+        assert_true(e.defaultPrevented, "during dispatch");
+    }), true);
+    TARGET.dispatchEvent(evt);
+
+    assert_true(evt.defaultPrevented, "after dispatch");
+    assert_equals(evt.target, TARGET);
+    assert_equals(evt.srcElement, TARGET);
+}, "Default prevention via returnValue");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-defaultPrevented.html b/testing/web-platform/tests/dom/events/Event-defaultPrevented.html
new file mode 100644
index 0000000000..2548fa3e06
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-defaultPrevented.html
@@ -0,0 +1,55 @@
+<!doctype html>
+<title>Event.defaultPrevented</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+var ev;
+test(function() {
+  ev = document.createEvent("Event");
+  assert_equals(ev.defaultPrevented, false, "defaultPrevented");
+}, "When an event is created, defaultPrevented should be initialized to false.");
+test(function() {
+  ev.initEvent("foo", true, false);
+  assert_equals(ev.bubbles, true, "bubbles");
+  assert_equals(ev.cancelable, false, "cancelable");
+  assert_equals(ev.defaultPrevented, false, "defaultPrevented");
+}, "initEvent should work correctly (not cancelable).");
+test(function() {
+  assert_equals(ev.cancelable, false, "cancelable (before)");
+  ev.preventDefault();
+  assert_equals(ev.cancelable, false, "cancelable (after)");
+  assert_equals(ev.defaultPrevented, false, "defaultPrevented");
+}, "preventDefault() should not change defaultPrevented if cancelable is false.");
+test(function() {
+  assert_equals(ev.cancelable, false, "cancelable (before)");
+  ev.returnValue = false;
+  assert_equals(ev.cancelable, false, "cancelable (after)");
+  assert_equals(ev.defaultPrevented, false, "defaultPrevented");
+}, "returnValue should not change defaultPrevented if cancelable is false.");
+test(function() {
+  ev.initEvent("foo", true, true);
+  assert_equals(ev.bubbles, true, "bubbles");
+  assert_equals(ev.cancelable, true, "cancelable");
+  assert_equals(ev.defaultPrevented, false, "defaultPrevented");
+}, "initEvent should work correctly (cancelable).");
+test(function() {
+  assert_equals(ev.cancelable, true, "cancelable (before)");
+  ev.preventDefault();
+  assert_equals(ev.cancelable, true, "cancelable (after)");
+  assert_equals(ev.defaultPrevented, true, "defaultPrevented");
+}, "preventDefault() should change defaultPrevented if cancelable is true.");
+test(function() {
+  ev.initEvent("foo", true, true);
+  assert_equals(ev.cancelable, true, "cancelable (before)");
+  ev.returnValue = false;
+  assert_equals(ev.cancelable, true, "cancelable (after)");
+  assert_equals(ev.defaultPrevented, true, "defaultPrevented");
+}, "returnValue should change defaultPrevented if cancelable is true.");
+test(function() {
+  ev.initEvent("foo", true, true);
+  assert_equals(ev.bubbles, true, "bubbles");
+  assert_equals(ev.cancelable, true, "cancelable");
+  assert_equals(ev.defaultPrevented, false, "defaultPrevented");
+}, "initEvent should unset defaultPrevented.");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-bubble-canceled.html b/testing/web-platform/tests/dom/events/Event-dispatch-bubble-canceled.html
new file mode 100644
index 0000000000..20f398f66f
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-bubble-canceled.html
@@ -0,0 +1,59 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title>Setting cancelBubble=true prior to dispatchEvent()</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+<div id="log"></div>
+
+<table id="table" border="1" style="display: none">
+    <tbody id="table-body">
+    <tr id="table-row">
+        <td id="table-cell">Shady Grove</td>
+        <td>Aeolian</td>
+    </tr>
+    <tr id="parent">
+        <td id="target">Over the river, Charlie</td>
+        <td>Dorian</td>
+    </tr>
+    </tbody>
+</table>
+
+<script>
+test(function() {
+    var event = "foo";
+    var target = document.getElementById("target");
+    var parent = document.getElementById("parent");
+    var tbody = document.getElementById("table-body");
+    var table = document.getElementById("table");
+    var body = document.body;
+    var html = document.documentElement;
+    var current_targets = [window, document, html, body, table, tbody, parent, target];
+    var expected_targets = [];
+    var actual_targets = [];
+    var expected_phases = [];
+    var actual_phases = [];
+
+    var test_event = function(evt) {
+        actual_targets.push(evt.currentTarget);
+        actual_phases.push(evt.eventPhase);
+    };
+
+    for (var i = 0; i < current_targets.length; ++i) {
+        current_targets[i].addEventListener(event, test_event, true);
+        current_targets[i].addEventListener(event, test_event, false);
+    }
+
+    var evt = document.createEvent("Event");
+    evt.initEvent(event, true, true);
+    evt.cancelBubble = true;
+    target.dispatchEvent(evt);
+
+    assert_array_equals(actual_targets, expected_targets, "actual_targets");
+    assert_array_equals(actual_phases, expected_phases, "actual_phases");
+});
+</script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-bubbles-false.html b/testing/web-platform/tests/dom/events/Event-dispatch-bubbles-false.html
new file mode 100644
index 0000000000..0f43cb0275
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-bubbles-false.html
@@ -0,0 +1,98 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title> Event.bubbles attribute is set to false </title>
+<link rel="help" href="https://dom.spec.whatwg.org/#dom-event-initevent">
+<link rel="help" href="https://dom.spec.whatwg.org/#concept-event-dispatch">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id=log></div>
+<table id="table" border="1" style="display: none">
+    <tbody id="table-body">
+    <tr id="table-row">
+        <td id="table-cell">Shady Grove</td>
+        <td>Aeolian</td>
+    </tr>
+    <tr id="parent">
+        <td id="target">Over the river, Charlie</td>
+        <td>Dorian</td>
+    </tr>
+    </tbody>
+</table>
+<script>
+function targetsForDocumentChain(document) {
+    return [
+        document,
+        document.documentElement,
+        document.getElementsByTagName("body")[0],
+        document.getElementById("table"),
+        document.getElementById("table-body"),
+        document.getElementById("parent")
+    ];
+}
+
+function testChain(document, targetParents, phases, event_type) {
+    var target = document.getElementById("target");
+    var targets = targetParents.concat(target);
+    var expected_targets = targets.concat(target);
+
+    var actual_targets = [], actual_phases = [];
+    var test_event = function(evt) {
+        actual_targets.push(evt.currentTarget);
+        actual_phases.push(evt.eventPhase);
+    }
+
+    for (var i = 0; i < targets.length; i++) {
+        targets[i].addEventListener(event_type, test_event, true);
+        targets[i].addEventListener(event_type, test_event, false);
+    }
+
+    var evt = document.createEvent("Event");
+    evt.initEvent(event_type, false, true);
+
+    target.dispatchEvent(evt);
+
+    assert_array_equals(actual_targets, expected_targets, "targets");
+    assert_array_equals(actual_phases, phases, "phases");
+}
+
+var phasesForDocumentChain = [
+    Event.CAPTURING_PHASE,
+    Event.CAPTURING_PHASE,
+    Event.CAPTURING_PHASE,
+    Event.CAPTURING_PHASE,
+    Event.CAPTURING_PHASE,
+    Event.CAPTURING_PHASE,
+    Event.AT_TARGET,
+    Event.AT_TARGET,
+];
+
+test(function () {
+    var chainWithWindow = [window].concat(targetsForDocumentChain(document));
+    testChain(
+        document, chainWithWindow, [Event.CAPTURING_PHASE].concat(phasesForDocumentChain), "click");
+}, "In window.document with click event");
+
+test(function () {
+    testChain(document, targetsForDocumentChain(document), phasesForDocumentChain, "load");
+}, "In window.document with load event")
+
+test(function () {
+    var documentClone = document.cloneNode(true);
+    testChain(
+        documentClone, targetsForDocumentChain(documentClone), phasesForDocumentChain, "click");
+}, "In window.document.cloneNode(true)");
+
+test(function () {
+    var newDocument = new Document();
+    newDocument.appendChild(document.documentElement.cloneNode(true));
+    testChain(
+        newDocument, targetsForDocumentChain(newDocument), phasesForDocumentChain, "click");
+}, "In new Document()");
+
+test(function () {
+    var HTMLDocument = document.implementation.createHTMLDocument();
+    HTMLDocument.body.appendChild(document.getElementById("table").cloneNode(true));
+    testChain(
+        HTMLDocument, targetsForDocumentChain(HTMLDocument), phasesForDocumentChain, "click");
+}, "In DOMImplementation.createHTMLDocument()");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-bubbles-true.html b/testing/web-platform/tests/dom/events/Event-dispatch-bubbles-true.html
new file mode 100644
index 0000000000..b23605a1eb
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-bubbles-true.html
@@ -0,0 +1,108 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title> Event.bubbles attribute is set to false </title>
+<link rel="help" href="https://dom.spec.whatwg.org/#dom-event-initevent">
+<link rel="help" href="https://dom.spec.whatwg.org/#concept-event-dispatch">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id=log></div>
+<table id="table" border="1" style="display: none">
+    <tbody id="table-body">
+    <tr id="table-row">
+        <td id="table-cell">Shady Grove</td>
+        <td>Aeolian</td>
+    </tr>
+    <tr id="parent">
+        <td id="target">Over the river, Charlie</td>
+        <td>Dorian</td>
+    </tr>
+    </tbody>
+</table>
+<script>
+function concatReverse(a) {
+    return a.concat(a.map(function(x) { return x }).reverse());
+}
+
+function targetsForDocumentChain(document) {
+    return [
+        document,
+        document.documentElement,
+        document.getElementsByTagName("body")[0],
+        document.getElementById("table"),
+        document.getElementById("table-body"),
+        document.getElementById("parent")
+    ];
+}
+
+function testChain(document, targetParents, phases, event_type) {
+    var target = document.getElementById("target");
+    var targets = targetParents.concat(target);
+    var expected_targets = concatReverse(targets);
+
+    var actual_targets = [], actual_phases = [];
+    var test_event = function(evt) {
+        actual_targets.push(evt.currentTarget);
+        actual_phases.push(evt.eventPhase);
+    }
+
+    for (var i = 0; i < targets.length; i++) {
+        targets[i].addEventListener(event_type, test_event, true);
+        targets[i].addEventListener(event_type, test_event, false);
+    }
+
+    var evt = document.createEvent("Event");
+    evt.initEvent(event_type, true, true);
+
+    target.dispatchEvent(evt);
+
+    assert_array_equals(actual_targets, expected_targets, "targets");
+    assert_array_equals(actual_phases, phases, "phases");
+}
+
+var phasesForDocumentChain = [
+    Event.CAPTURING_PHASE,
+    Event.CAPTURING_PHASE,
+    Event.CAPTURING_PHASE,
+    Event.CAPTURING_PHASE,
+    Event.CAPTURING_PHASE,
+    Event.CAPTURING_PHASE,
+    Event.AT_TARGET,
+    Event.AT_TARGET,
+    Event.BUBBLING_PHASE,
+    Event.BUBBLING_PHASE,
+    Event.BUBBLING_PHASE,
+    Event.BUBBLING_PHASE,
+    Event.BUBBLING_PHASE,
+    Event.BUBBLING_PHASE,
+];
+
+test(function () {
+    var chainWithWindow = [window].concat(targetsForDocumentChain(document));
+    var phases = [Event.CAPTURING_PHASE].concat(phasesForDocumentChain, Event.BUBBLING_PHASE);
+    testChain(document, chainWithWindow, phases, "click");
+}, "In window.document with click event");
+
+test(function () {
+    testChain(document, targetsForDocumentChain(document), phasesForDocumentChain, "load");
+}, "In window.document with load event")
+
+test(function () {
+    var documentClone = document.cloneNode(true);
+    testChain(
+        documentClone, targetsForDocumentChain(documentClone), phasesForDocumentChain, "click");
+}, "In window.document.cloneNode(true)");
+
+test(function () {
+    var newDocument = new Document();
+    newDocument.appendChild(document.documentElement.cloneNode(true));
+    testChain(
+        newDocument, targetsForDocumentChain(newDocument), phasesForDocumentChain, "click");
+}, "In new Document()");
+
+test(function () {
+    var HTMLDocument = document.implementation.createHTMLDocument();
+    HTMLDocument.body.appendChild(document.getElementById("table").cloneNode(true));
+    testChain(
+        HTMLDocument, targetsForDocumentChain(HTMLDocument), phasesForDocumentChain, "click");
+}, "In DOMImplementation.createHTMLDocument()");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-click.html b/testing/web-platform/tests/dom/events/Event-dispatch-click.html
new file mode 100644
index 0000000000..010305775d
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-click.html
@@ -0,0 +1,369 @@
+<!doctype html>
+<title>Synthetic click event "magic"</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id=log></div>
+<div id=dump style=display:none></div>
+<script>
+var dump = document.getElementById("dump")
+
+async_test(function(t) {
+  var input = document.createElement("input")
+  input.type = "checkbox"
+  dump.appendChild(input)
+  input.onclick = t.step_func_done(function() {
+    assert_true(input.checked)
+  })
+  input.click()
+}, "basic with click()")
+
+async_test(function(t) {
+  var input = document.createElement("input")
+  input.type = "checkbox"
+  dump.appendChild(input)
+  input.onclick = t.step_func_done(function() {
+    assert_true(input.checked)
+  })
+  input.dispatchEvent(new MouseEvent("click", {bubbles:true})) // equivalent to the above
+}, "basic with dispatchEvent()")
+
+async_test(function(t) {
+  var input = document.createElement("input")
+  input.type = "checkbox"
+  dump.appendChild(input)
+  input.onclick = t.step_func_done(function() {
+    assert_false(input.checked)
+  })
+  input.dispatchEvent(new Event("click", {bubbles:true})) // no MouseEvent
+}, "basic with wrong event class")
+
+async_test(function(t) {
+  var input = document.createElement("input")
+  input.type = "checkbox"
+  dump.appendChild(input)
+  var child = input.appendChild(new Text("does not matter"))
+  child.dispatchEvent(new MouseEvent("click")) // does not bubble
+  assert_false(input.checked)
+  t.done()
+}, "look at parents only when event bubbles")
+
+async_test(function(t) {
+  var input = document.createElement("input")
+  input.type = "checkbox"
+  dump.appendChild(input)
+  input.onclick = t.step_func_done(function() {
+    assert_true(input.checked)
+  })
+  var child = input.appendChild(new Text("does not matter"))
+  child.dispatchEvent(new MouseEvent("click", {bubbles:true}))
+}, "look at parents when event bubbles")
+
+async_test(function(t) {
+  var input = document.createElement("input")
+  input.type = "checkbox"
+  dump.appendChild(input)
+  input.onclick = t.step_func(function() {
+    assert_false(input.checked, "input pre-click must not be triggered")
+  })
+  var child = input.appendChild(document.createElement("input"))
+  child.type = "checkbox"
+  child.onclick = t.step_func(function() {
+    assert_true(child.checked, "child pre-click must be triggered")
+  })
+  child.dispatchEvent(new MouseEvent("click", {bubbles:true}))
+  t.done()
+}, "pick the first with activation behavior <input type=checkbox>")
+
+async_test(function(t) { // as above with <a>
+  window.hrefComplete = t.step_func(function(a) {
+    assert_equals(a, 'child');
+    t.done();
+  });
+  var link = document.createElement("a")
+  link.href = "javascript:hrefComplete('link')" // must not be triggered
+  dump.appendChild(link)
+  var child = link.appendChild(document.createElement("a"))
+  child.href = "javascript:hrefComplete('child')"
+  child.dispatchEvent(new MouseEvent("click", {bubbles:true}))
+}, "pick the first with activation behavior <a href>")
+
+async_test(function(t) {
+  var input = document.createElement("input")
+  input.type = "checkbox"
+  dump.appendChild(input)
+  var clickEvent = new MouseEvent("click")
+  input.onchange = t.step_func_done(function() {
+    assert_false(clickEvent.defaultPrevented)
+    assert_true(clickEvent.returnValue)
+    assert_equals(clickEvent.eventPhase, 0)
+    assert_equals(clickEvent.currentTarget, null)
+    assert_equals(clickEvent.target, input)
+    assert_equals(clickEvent.srcElement, input)
+    assert_equals(clickEvent.composedPath().length, 0)
+  })
+  input.dispatchEvent(clickEvent)
+}, "event state during post-click handling")
+
+async_test(function(t) {
+  var input = document.createElement("input")
+  input.type = "checkbox"
+  dump.appendChild(input)
+  var clickEvent = new MouseEvent("click")
+  var finalTarget = document.createElement("doesnotmatter")
+  finalTarget.onclick = t.step_func_done(function() {
+    assert_equals(clickEvent.target, finalTarget)
+    assert_equals(clickEvent.srcElement, finalTarget)
+  })
+  input.onchange = t.step_func(function() {
+    finalTarget.dispatchEvent(clickEvent)
+  })
+  input.dispatchEvent(clickEvent)
+}, "redispatch during post-click handling")
+
+async_test(function(t) {
+  var input = document.createElement("input")
+  input.type = "checkbox"
+  dump.appendChild(input)
+  var child = input.appendChild(document.createElement("input"))
+  child.type = "checkbox"
+  child.disabled = true
+  child.click()
+  assert_false(input.checked)
+  assert_false(child.checked)
+  t.done()
+}, "disabled checkbox still has activation behavior")
+
+async_test(function(t) {
+  var state = "start"
+
+  var form = document.createElement("form")
+  form.onsubmit = t.step_func(() => {
+    if(state == "start" || state == "checkbox") {
+      state = "failure"
+    } else if(state == "form") {
+      state = "done"
+    }
+    return false
+  })
+  dump.appendChild(form)
+  var button = form.appendChild(document.createElement("button"))
+  button.type = "submit"
+  var checkbox = button.appendChild(document.createElement("input"))
+  checkbox.type = "checkbox"
+  checkbox.onclick = t.step_func(() => {
+    if(state == "start") {
+      assert_unreached()
+    } else if(state == "checkbox") {
+      assert_true(checkbox.checked)
+    }
+  })
+  checkbox.disabled = true
+  checkbox.click()
+  assert_equals(state, "start")
+
+  state = "checkbox"
+  checkbox.disabled = false
+  checkbox.click()
+  assert_equals(state, "checkbox")
+
+  state = "form"
+  button.click()
+  assert_equals(state, "done")
+
+  t.done()
+}, "disabled checkbox still has activation behavior, part 2")
+
+async_test(function(t) {
+  var input = document.createElement("input")
+  input.type = "checkbox"
+  input.onclick = t.step_func_done(function() {
+    assert_true(input.checked)
+  })
+  input.click()
+}, "disconnected checkbox should be checked")
+
+async_test(function(t) {
+  var input = document.createElement("input")
+  input.type = "radio"
+  input.onclick = t.step_func_done(function() {
+    assert_true(input.checked)
+  })
+  input.click()
+}, "disconnected radio should be checked")
+
+async_test(t => {
+  const input = document.createElement('input');
+  input.type = 'checkbox';
+  input.onclick = t.step_func_done(() => {
+    assert_true(input.checked);
+  });
+  input.dispatchEvent(new MouseEvent('click'));
+}, `disconnected checkbox should be checked from dispatchEvent(new MouseEvent('click'))`);
+
+async_test(t => {
+  const input = document.createElement('input');
+  input.type = 'radio';
+  input.onclick = t.step_func_done(() => {
+    assert_true(input.checked);
+  });
+  input.dispatchEvent(new MouseEvent('click'));
+}, `disconnected radio should be checked from dispatchEvent(new MouseEvent('click'))`);
+
+test(() => {
+  const input = document.createElement("input");
+  input.type = "checkbox";
+  input.disabled = true;
+  input.dispatchEvent(new MouseEvent("click"));
+  assert_true(input.checked);
+}, `disabled checkbox should be checked from dispatchEvent(new MouseEvent("click"))`);
+
+test(() => {
+  const input = document.createElement("input");
+  input.type = "radio";
+  input.disabled = true;
+  input.dispatchEvent(new MouseEvent("click"));
+  assert_true(input.checked);
+}, `disabled radio should be checked from dispatchEvent(new MouseEvent("click"))`);
+
+async_test(t => {
+  const input = document.createElement("input");
+  input.type = "checkbox";
+  input.disabled = true;
+  input.onclick = t.step_func_done();
+  input.dispatchEvent(new MouseEvent("click"));
+}, `disabled checkbox should fire onclick`);
+
+async_test(t => {
+  const input = document.createElement("input");
+  input.type = "radio";
+  input.disabled = true;
+  input.onclick = t.step_func_done();
+  input.dispatchEvent(new MouseEvent("click"));
+}, `disabled radio should fire onclick`);
+
+async_test(t => {
+  const input = document.createElement("input");
+  input.type = "checkbox";
+  input.disabled = true;
+  input.onclick = t.step_func(ev => {
+    assert_true(input.checked);
+    ev.preventDefault();
+    queueMicrotask(t.step_func_done(() => {
+      assert_false(input.checked);
+    }));
+  });
+  input.dispatchEvent(new MouseEvent("click", { cancelable: true }));
+}, `disabled checkbox should get legacy-canceled-activation behavior`);
+
+async_test(t => {
+  const input = document.createElement("input");
+  input.type = "radio";
+  input.disabled = true;
+  input.onclick = t.step_func(ev => {
+    assert_true(input.checked);
+    ev.preventDefault();
+    queueMicrotask(t.step_func_done(() => {
+      assert_false(input.checked);
+    }));
+  });
+  input.dispatchEvent(new MouseEvent("click", { cancelable: true }));
+}, `disabled radio should get legacy-canceled-activation behavior`);
+
+test(t => {
+  const input = document.createElement("input");
+  input.type = "checkbox";
+  input.disabled = true;
+  const ev = new MouseEvent("click", { cancelable: true });
+  ev.preventDefault();
+  input.dispatchEvent(ev);
+  assert_false(input.checked);
+}, `disabled checkbox should get legacy-canceled-activation behavior 2`);
+
+test(t => {
+  const input = document.createElement("input");
+  input.type = "radio";
+  input.disabled = true;
+  const ev = new MouseEvent("click", { cancelable: true });
+  ev.preventDefault();
+  input.dispatchEvent(ev);
+  assert_false(input.checked);
+}, `disabled radio should get legacy-canceled-activation behavior 2`);
+
+for (const type of ["checkbox", "radio"]) {
+  for (const handler of ["oninput", "onchange"]) {
+    async_test(t => {
+      const input = document.createElement("input");
+      input.type = type;
+      input.onclick = t.step_func(ev => {
+        input.disabled = true;
+      });
+      input[handler] = t.step_func(ev => {
+        assert_equals(input.checked, true);
+        t.done();
+      });
+      dump.append(input);
+      input.click();
+    }, `disabling ${type} in onclick listener shouldn't suppress ${handler}`);
+  }
+}
+
+async_test(function(t) {
+  var form = document.createElement("form")
+  var didSubmit = false
+  form.onsubmit = t.step_func(() => {
+    didSubmit = true
+    return false
+  })
+  var input = form.appendChild(document.createElement("input"))
+  input.type = "submit"
+  input.click()
+  assert_false(didSubmit)
+  t.done()
+}, "disconnected form should not submit")
+
+async_test(t => {
+  const form = document.createElement("form");
+  form.onsubmit = t.step_func(ev => {
+    ev.preventDefault();
+    assert_unreached("The form is unexpectedly submitted.");
+  });
+  dump.append(form);
+  const input = form.appendChild(document.createElement("input"));
+  input.type = "submit"
+  input.disabled = true;
+  input.dispatchEvent(new MouseEvent("click", { cancelable: true }));
+  t.done();
+}, "disabled submit button should not activate");
+
+async_test(t => {
+  const form = document.createElement("form");
+  form.onsubmit = t.step_func(ev => {
+    ev.preventDefault();
+    assert_unreached("The form is unexpectedly submitted.");
+  });
+  dump.append(form);
+  const input = form.appendChild(document.createElement("input"));
+  input.onclick = t.step_func(() => {
+    input.disabled = true;
+  });
+  input.type = "submit"
+  input.dispatchEvent(new MouseEvent("click", { cancelable: true }));
+  t.done();
+}, "submit button should not activate if the event listener disables it");
+
+async_test(t => {
+  const form = document.createElement("form");
+  form.onsubmit = t.step_func(ev => {
+    ev.preventDefault();
+    assert_unreached("The form is unexpectedly submitted.");
+  });
+  dump.append(form);
+  const input = form.appendChild(document.createElement("input"));
+  input.onclick = t.step_func(() => {
+    input.type = "submit"
+    input.disabled = true;
+  });
+  input.click();
+  t.done();
+}, "submit button that morphed from checkbox should not activate");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-click.tentative.html b/testing/web-platform/tests/dom/events/Event-dispatch-click.tentative.html
new file mode 100644
index 0000000000..cfdae55ef2
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-click.tentative.html
@@ -0,0 +1,78 @@
+<!doctype html>
+<title>Clicks on input element</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id=dump style=display:none></div>
+<script>
+var dump = document.getElementById("dump")
+
+test(t => {
+  const input = document.createElement("input");
+  input.type = "checkbox";
+  input.disabled = true;
+  const label = document.createElement("label");
+  label.append(input);
+  dump.append(label);
+  label.click();
+  assert_false(input.checked);
+}, "disabled checkbox should not be checked from label click");
+
+test(t => {
+  const input = document.createElement("input");
+  input.type = "radio";
+  input.disabled = true;
+  const label = document.createElement("label");
+  label.append(input);
+  dump.append(label);
+  label.click();
+  assert_false(input.checked);
+}, "disabled radio should not be checked from label click");
+
+test(t => {
+  const input = document.createElement("input");
+  input.type = "checkbox";
+  input.disabled = true;
+  const label = document.createElement("label");
+  label.append(input);
+  dump.append(label);
+  label.dispatchEvent(new MouseEvent("click"));
+  assert_false(input.checked);
+}, "disabled checkbox should not be checked from label click by dispatchEvent");
+
+test(t => {
+  const input = document.createElement("input");
+  input.type = "radio";
+  input.disabled = true;
+  const label = document.createElement("label");
+  label.append(input);
+  dump.append(label);
+  label.dispatchEvent(new MouseEvent("click"));
+  assert_false(input.checked);
+}, "disabled radio should not be checked from label click by dispatchEvent");
+
+test(t => {
+  const checkbox = dump.appendChild(document.createElement("input"));
+  checkbox.type = "checkbox";
+  checkbox.onclick = ev => {
+    checkbox.type = "date";
+    ev.preventDefault();
+  };
+  checkbox.dispatchEvent(new MouseEvent("click", { cancelable: true }));
+  assert_false(checkbox.checked);
+}, "checkbox morphed into another type should not mutate checked state");
+
+test(t => {
+  const radio1 = dump.appendChild(document.createElement("input"));
+  const radio2 = dump.appendChild(radio1.cloneNode());
+  radio1.type = radio2.type = "radio";
+  radio1.name = radio2.name = "foo";
+  radio2.checked = true;
+  radio1.onclick = ev => {
+    radio1.type = "date";
+    ev.preventDefault();
+  };
+  radio1.dispatchEvent(new MouseEvent("click", { cancelable: true }));
+  assert_false(radio1.checked);
+  assert_true(radio2.checked);
+}, "radio morphed into another type should not steal the existing checked state");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-detached-click.html b/testing/web-platform/tests/dom/events/Event-dispatch-detached-click.html
new file mode 100644
index 0000000000..76ea3d78ba
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-detached-click.html
@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+<title>Click event on an element not in the document</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id=log></div>
+<script>
+test(function() {
+  var EVENT = "click";
+  var TARGET = document.createElement("somerandomelement");
+  var t = async_test("Click event can be dispatched to an element that is not in the document.")
+  TARGET.addEventListener(EVENT, t.step_func(function(evt) {
+    assert_equals(evt.target, TARGET);
+    assert_equals(evt.srcElement, TARGET);
+    t.done();
+  }), true);
+  var e = document.createEvent("Event");
+  e.initEvent(EVENT, true, true);
+  TARGET.dispatchEvent(e);
+});
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-detached-input-and-change.html b/testing/web-platform/tests/dom/events/Event-dispatch-detached-input-and-change.html
new file mode 100644
index 0000000000..a53ae71ac2
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-detached-input-and-change.html
@@ -0,0 +1,190 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<link rel="author" title="Joey Arhar" href="mailto:jarhar@chromium.org">
+<title>input and change events for detached checkbox and radio elements</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body>
+<script>
+
+test(() => {
+  const input = document.createElement('input');
+  input.type = 'checkbox';
+
+  let inputEventFired = false;
+  input.addEventListener('input', () => inputEventFired = true);
+  let changeEventFired = false;
+  input.addEventListener('change', () => changeEventFired = true);
+  input.click();
+  assert_false(inputEventFired);
+  assert_false(changeEventFired);
+}, 'detached checkbox should not emit input or change events on click().');
+
+test(() => {
+  const input = document.createElement('input');
+  input.type = 'radio';
+
+  let inputEventFired = false;
+  input.addEventListener('input', () => inputEventFired = true);
+  let changeEventFired = false;
+  input.addEventListener('change', () => changeEventFired = true);
+  input.click();
+  assert_false(inputEventFired);
+  assert_false(changeEventFired);
+}, 'detached radio should not emit input or change events on click().');
+
+test(() => {
+  const input = document.createElement('input');
+  input.type = 'checkbox';
+
+  let inputEventFired = false;
+  input.addEventListener('input', () => inputEventFired = true);
+  let changeEventFired = false;
+  input.addEventListener('change', () => changeEventFired = true);
+  input.dispatchEvent(new MouseEvent('click'));
+  assert_false(inputEventFired);
+  assert_false(changeEventFired);
+}, `detached checkbox should not emit input or change events on dispatchEvent(new MouseEvent('click')).`);
+
+test(() => {
+  const input = document.createElement('input');
+  input.type = 'radio';
+
+  let inputEventFired = false;
+  input.addEventListener('input', () => inputEventFired = true);
+  let changeEventFired = false;
+  input.addEventListener('change', () => changeEventFired = true);
+  input.dispatchEvent(new MouseEvent('click'));
+  assert_false(inputEventFired);
+  assert_false(changeEventFired);
+}, `detached radio should not emit input or change events on dispatchEvent(new MouseEvent('click')).`);
+
+
+test(() => {
+  const input = document.createElement('input');
+  input.type = 'checkbox';
+  document.body.appendChild(input);
+
+  let inputEventFired = false;
+  input.addEventListener('input', () => inputEventFired = true);
+  let changeEventFired = false;
+  input.addEventListener('change', () => changeEventFired = true);
+  input.click();
+  assert_true(inputEventFired);
+  assert_true(changeEventFired);
+}, 'attached checkbox should emit input and change events on click().');
+
+test(() => {
+  const input = document.createElement('input');
+  input.type = 'radio';
+  document.body.appendChild(input);
+
+  let inputEventFired = false;
+  input.addEventListener('input', () => inputEventFired = true);
+  let changeEventFired = false;
+  input.addEventListener('change', () => changeEventFired = true);
+  input.click();
+  assert_true(inputEventFired);
+  assert_true(changeEventFired);
+}, 'attached radio should emit input and change events on click().');
+
+test(() => {
+  const input = document.createElement('input');
+  input.type = 'checkbox';
+  document.body.appendChild(input);
+
+  let inputEventFired = false;
+  input.addEventListener('input', () => inputEventFired = true);
+  let changeEventFired = false;
+  input.addEventListener('change', () => changeEventFired = true);
+  input.dispatchEvent(new MouseEvent('click'));
+  assert_true(inputEventFired);
+  assert_true(changeEventFired);
+}, `attached checkbox should emit input and change events on dispatchEvent(new MouseEvent('click')).`);
+
+test(() => {
+  const input = document.createElement('input');
+  input.type = 'radio';
+  document.body.appendChild(input);
+
+  let inputEventFired = false;
+  input.addEventListener('input', () => inputEventFired = true);
+  let changeEventFired = false;
+  input.addEventListener('change', () => changeEventFired = true);
+  input.dispatchEvent(new MouseEvent('click'));
+  assert_true(inputEventFired);
+  assert_true(changeEventFired);
+}, `attached radio should emit input and change events on dispatchEvent(new MouseEvent('click')).`);
+
+
+test(() => {
+  const input = document.createElement('input');
+  input.type = 'checkbox';
+  const shadowHost = document.createElement('div');
+  document.body.appendChild(shadowHost);
+  const shadowRoot = shadowHost.attachShadow({mode: 'open'});
+  shadowRoot.appendChild(input);
+
+  let inputEventFired = false;
+  input.addEventListener('input', () => inputEventFired = true);
+  let changeEventFired = false;
+  input.addEventListener('change', () => changeEventFired = true);
+  input.click();
+  assert_true(inputEventFired);
+  assert_true(changeEventFired);
+}, 'attached to shadow dom checkbox should emit input and change events on click().');
+
+test(() => {
+  const input = document.createElement('input');
+  input.type = 'radio';
+  const shadowHost = document.createElement('div');
+  document.body.appendChild(shadowHost);
+  const shadowRoot = shadowHost.attachShadow({mode: 'open'});
+  shadowRoot.appendChild(input);
+
+  let inputEventFired = false;
+  input.addEventListener('input', () => inputEventFired = true);
+  let changeEventFired = false;
+  input.addEventListener('change', () => changeEventFired = true);
+  input.click();
+  assert_true(inputEventFired);
+  assert_true(changeEventFired);
+}, 'attached to shadow dom radio should emit input and change events on click().');
+
+test(() => {
+  const input = document.createElement('input');
+  input.type = 'checkbox';
+  const shadowHost = document.createElement('div');
+  document.body.appendChild(shadowHost);
+  const shadowRoot = shadowHost.attachShadow({mode: 'open'});
+  shadowRoot.appendChild(input);
+
+  let inputEventFired = false;
+  input.addEventListener('input', () => inputEventFired = true);
+  let changeEventFired = false;
+  input.addEventListener('change', () => changeEventFired = true);
+  input.dispatchEvent(new MouseEvent('click'));
+  assert_true(inputEventFired);
+  assert_true(changeEventFired);
+}, `attached to shadow dom checkbox should emit input and change events on dispatchEvent(new MouseEvent('click')).`);
+
+test(() => {
+  const input = document.createElement('input');
+  input.type = 'radio';
+  const shadowHost = document.createElement('div');
+  document.body.appendChild(shadowHost);
+  const shadowRoot = shadowHost.attachShadow({mode: 'open'});
+  shadowRoot.appendChild(input);
+
+  let inputEventFired = false;
+  input.addEventListener('input', () => inputEventFired = true);
+  let changeEventFired = false;
+  input.addEventListener('change', () => changeEventFired = true);
+  input.dispatchEvent(new MouseEvent('click'));
+  assert_true(inputEventFired);
+  assert_true(changeEventFired);
+}, `attached to shadow dom radio should emit input and change events on dispatchEvent(new MouseEvent('click')).`);
+
+</script>
+</body>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-handlers-changed.html b/testing/web-platform/tests/dom/events/Event-dispatch-handlers-changed.html
new file mode 100644
index 0000000000..24e6fd70cb
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-handlers-changed.html
@@ -0,0 +1,91 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title> Dispatch additional events inside an event listener </title>
+<link rel="help" href="https://dom.spec.whatwg.org/#concept-event-dispatch">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id=log></div>
+
+<table id="table" border="1" style="display: none">
+    <tbody id="table-body">
+    <tr id="table-row">
+        <td id="table-cell">Shady Grove</td>
+        <td>Aeolian</td>
+    </tr>
+    <tr id="parent">
+        <td id="target">Over the river, Charlie</td>
+        <td>Dorian</td>
+    </tr>
+    </tbody>
+</table>
+
+<script>
+test(function() {
+  var event_type = "bar";
+  var target = document.getElementById("target");
+  var parent = document.getElementById("parent");
+  var tbody = document.getElementById("table-body");
+  var table = document.getElementById("table");
+  var body = document.body;
+  var html = document.documentElement;
+  var targets = [window, document, html, body, table, tbody, parent, target];
+  var expected_targets = [
+    window,
+    document,
+    html,
+    body,
+    table,
+    tbody,
+    parent,
+    target,
+    target,
+    target, // The additional listener for target runs as we copy its listeners twice
+    parent,
+    tbody,
+    table,
+    body,
+    html,
+    document,
+    window
+  ];
+  var expected_listeners = [0,0,0,0,0,0,0,0,1,3,1,1,1,1,1,1,1];
+
+  var actual_targets = [], actual_listeners = [];
+  var test_event_function = function(i) {
+    return this.step_func(function(evt) {
+      actual_targets.push(evt.currentTarget);
+      actual_listeners.push(i);
+
+      if (evt.eventPhase != evt.BUBBLING_PHASE && evt.currentTarget.foo != 1) {
+        evt.currentTarget.removeEventListener(event_type, event_handlers[0], true);
+        evt.currentTarget.addEventListener(event_type, event_handlers[2], true);
+        evt.currentTarget.foo = 1;
+      }
+
+      if (evt.eventPhase != evt.CAPTURING_PHASE && evt.currentTarget.foo != 3) {
+        evt.currentTarget.removeEventListener(event_type, event_handlers[0], false);
+        evt.currentTarget.addEventListener(event_type, event_handlers[3], false);
+        evt.currentTarget.foo = 3;
+      }
+    });
+  }.bind(this);
+  var event_handlers = [
+    test_event_function(0),
+    test_event_function(1),
+    test_event_function(2),
+    test_event_function(3),
+  ];
+
+  for (var i = 0; i < targets.length; ++i) {
+    targets[i].addEventListener(event_type, event_handlers[0], true);
+    targets[i].addEventListener(event_type, event_handlers[1], false);
+  }
+
+  var evt = document.createEvent("Event");
+  evt.initEvent(event_type, true, true);
+  target.dispatchEvent(evt);
+
+  assert_array_equals(actual_targets, expected_targets, "actual_targets");
+  assert_array_equals(actual_listeners, expected_listeners, "actual_listeners");
+});
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-listener-order.window.js b/testing/web-platform/tests/dom/events/Event-dispatch-listener-order.window.js
new file mode 100644
index 0000000000..a01a472872
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-listener-order.window.js
@@ -0,0 +1,20 @@
+test(t => {
+  const hostParent = document.createElement("section"),
+        host = hostParent.appendChild(document.createElement("div")),
+        shadowRoot = host.attachShadow({ mode: "closed" }),
+        targetParent = shadowRoot.appendChild(document.createElement("p")),
+        target = targetParent.appendChild(document.createElement("span")),
+        path = [hostParent, host, shadowRoot, targetParent, target],
+        expected = [],
+        result = [];
+  path.forEach((node, index) => {
+    expected.splice(index, 0, "capturing " + node.nodeName);
+    expected.splice(index + 1, 0, "bubbling " + node.nodeName);
+  });
+  path.forEach(node => {
+    node.addEventListener("test", () => { result.push("bubbling " + node.nodeName) });
+    node.addEventListener("test", () => { result.push("capturing " + node.nodeName) }, true);
+  });
+  target.dispatchEvent(new CustomEvent('test', { detail: {}, bubbles: true, composed: true }));
+  assert_array_equals(result, expected);
+});
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-multiple-cancelBubble.html b/testing/web-platform/tests/dom/events/Event-dispatch-multiple-cancelBubble.html
new file mode 100644
index 0000000000..2873fd7794
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-multiple-cancelBubble.html
@@ -0,0 +1,51 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title>Multiple dispatchEvent() and cancelBubble</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+<div id=log></div>
+
+<div id="parent" style="display: none">
+    <input id="target" type="hidden" value=""/>
+</div>
+
+<script>
+test(function() {
+    var event_type = "foo";
+    var target = document.getElementById("target");
+    var parent = document.getElementById("parent");
+    var actual_result;
+    var test_event = function(evt) {
+        actual_result.push(evt.currentTarget);
+
+        if (parent == evt.currentTarget) {
+            evt.cancelBubble = true;
+        }
+    };
+
+    var evt = document.createEvent("Event");
+    evt.initEvent(event_type, true, true);
+
+    target.addEventListener(event_type, test_event, false);
+    parent.addEventListener(event_type, test_event, false);
+    document.addEventListener(event_type, test_event, false);
+    window.addEventListener(event_type, test_event, false);
+
+    actual_result = [];
+    target.dispatchEvent(evt);
+    assert_array_equals(actual_result, [target, parent]);
+
+    actual_result = [];
+    parent.dispatchEvent(evt);
+    assert_array_equals(actual_result, [parent]);
+
+    actual_result = [];
+    document.dispatchEvent(evt);
+    assert_array_equals(actual_result, [document, window]);
+});
+</script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-multiple-stopPropagation.html b/testing/web-platform/tests/dom/events/Event-dispatch-multiple-stopPropagation.html
new file mode 100644
index 0000000000..72644bd861
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-multiple-stopPropagation.html
@@ -0,0 +1,51 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title> Multiple dispatchEvent() and stopPropagation() </title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+<div id=log></div>
+
+<div id="parent" style="display: none">
+    <input id="target" type="hidden" value=""/>
+</div>
+
+<script>
+test(function() {
+    var event_type = "foo";
+    var target = document.getElementById("target");
+    var parent = document.getElementById("parent");
+    var actual_result;
+    var test_event = function(evt) {
+        actual_result.push(evt.currentTarget);
+
+        if (parent == evt.currentTarget) {
+            evt.stopPropagation();
+        }
+    };
+
+    var evt = document.createEvent("Event");
+    evt.initEvent(event_type, true, true);
+
+    target.addEventListener(event_type, test_event, false);
+    parent.addEventListener(event_type, test_event, false);
+    document.addEventListener(event_type, test_event, false);
+    window.addEventListener(event_type, test_event, false);
+
+    actual_result = [];
+    target.dispatchEvent(evt);
+    assert_array_equals(actual_result, [target, parent]);
+
+    actual_result = [];
+    parent.dispatchEvent(evt);
+    assert_array_equals(actual_result, [parent]);
+
+    actual_result = [];
+    document.dispatchEvent(evt);
+    assert_array_equals(actual_result, [document, window]);
+});
+</script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-omitted-capture.html b/testing/web-platform/tests/dom/events/Event-dispatch-omitted-capture.html
new file mode 100644
index 0000000000..77074d9a3e
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-omitted-capture.html
@@ -0,0 +1,70 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>EventTarget.addEventListener: capture argument omitted</title>
+<link rel="help" href="https://dom.spec.whatwg.org/#dom-eventtarget-addeventlistener">
+<link rel="help" href="https://dom.spec.whatwg.org/#concept-event-dispatch">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id=log></div>
+<table id="table" border="1" style="display: none">
+    <tbody id="table-body">
+    <tr id="table-row">
+        <td id="table-cell">Shady Grove</td>
+        <td>Aeolian</td>
+    </tr>
+    <tr id="parent">
+        <td id="target">Over the river, Charlie</td>
+        <td>Dorian</td>
+    </tr>
+    </tbody>
+</table>
+<script>
+test(function() {
+    var event_type = "foo";
+    var target = document.getElementById("target");
+    var targets = [
+        target,
+        document.getElementById("parent"),
+        document.getElementById("table-body"),
+        document.getElementById("table"),
+        document.body,
+        document.documentElement,
+        document,
+        window
+    ];
+    var phases = [
+        Event.AT_TARGET,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE
+    ];
+
+    var actual_targets = [], actual_phases = [];
+    var test_event = function(evt) {
+        actual_targets.push(evt.currentTarget);
+        actual_phases.push(evt.eventPhase);
+    }
+
+    for (var i = 0; i < targets.length; i++) {
+        targets[i].addEventListener(event_type, test_event);
+    }
+
+    var evt = document.createEvent("Event");
+    evt.initEvent(event_type, true, true);
+
+    target.dispatchEvent(evt);
+
+    for (var i = 0; i < targets.length; i++) {
+        targets[i].removeEventListener(event_type, test_event);
+    }
+
+    target.dispatchEvent(evt);
+
+    assert_array_equals(actual_targets, targets, "targets");
+    assert_array_equals(actual_phases, phases, "phases");
+}, "EventTarget.addEventListener with the capture argument omitted");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-on-disabled-elements.html b/testing/web-platform/tests/dom/events/Event-dispatch-on-disabled-elements.html
new file mode 100644
index 0000000000..361006a724
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-on-disabled-elements.html
@@ -0,0 +1,251 @@
+<!doctype html>
+<meta charset="utf8">
+<meta name="timeout" content="long">
+<title>Events must dispatch on disabled elements</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<style>
+  @keyframes fade {
+    0% {
+      opacity: 1;
+    }
+    100% {
+      opacity: 0;
+    }
+  }
+</style>
+<body>
+<script>
+// HTML elements that can be disabled
+const formElements = ["button", "fieldset", "input", "select", "textarea"];
+
+test(() => {
+  for (const localName of formElements) {
+    const elem = document.createElement(localName);
+    elem.disabled = true;
+    // pass becomes true if the event is called and it's the right type.
+    let pass = false;
+    const listener = ({ type }) => {
+      pass = type === "click";
+    };
+    elem.addEventListener("click", listener, { once: true });
+    elem.dispatchEvent(new Event("click"));
+    assert_true(
+      pass,
+      `Untrusted "click" Event didn't dispatch on ${elem.constructor.name}.`
+    );
+  }
+}, "Can dispatch untrusted 'click' Events at disabled HTML elements.");
+
+test(() => {
+  for (const localName of formElements) {
+    const elem = document.createElement(localName);
+    elem.disabled = true;
+    // pass becomes true if the event is called and it's the right type.
+    let pass = false;
+    const listener = ({ type }) => {
+      pass = type === "pass";
+    };
+    elem.addEventListener("pass", listener, { once: true });
+    elem.dispatchEvent(new Event("pass"));
+    assert_true(
+      pass,
+      `Untrusted "pass" Event didn't dispatch on ${elem.constructor.name}`
+    );
+  }
+}, "Can dispatch untrusted Events at disabled HTML elements.");
+
+test(() => {
+  for (const localName of formElements) {
+    const elem = document.createElement(localName);
+    elem.disabled = true;
+    // pass becomes true if the event is called and it's the right type.
+    let pass = false;
+    const listener = ({ type }) => {
+      pass = type === "custom-pass";
+    };
+    elem.addEventListener("custom-pass", listener, { once: true });
+    elem.dispatchEvent(new CustomEvent("custom-pass"));
+    assert_true(
+      pass,
+      `CustomEvent "custom-pass" didn't dispatch on ${elem.constructor.name}`
+    );
+  }
+}, "Can dispatch CustomEvents at disabled HTML elements.");
+
+test(() => {
+  for (const localName of formElements) {
+    const elem = document.createElement(localName);
+
+    // Element is disabled... so this click() MUST NOT fire an event.
+    elem.disabled = true;
+    let pass = true;
+    elem.onclick = e => {
+      pass = false;
+    };
+    elem.click();
+    assert_true(
+      pass,
+      `.click() must not dispatch "click" event on disabled ${
+        elem.constructor.name
+      }.`
+    );
+
+    // Element is (re)enabled... so this click() fires an event.
+    elem.disabled = false;
+    pass = false;
+    elem.onclick = e => {
+      pass = true;
+    };
+    elem.click();
+    assert_true(
+      pass,
+      `.click() must dispatch "click" event on enabled ${
+        elem.constructor.name
+      }.`
+    );
+  }
+}, "Calling click() on disabled elements must not dispatch events.");
+
+promise_test(async () => {
+  // For each form element type, set up transition event handlers.
+  for (const localName of formElements) {
+    const elem = document.createElement(localName);
+    elem.disabled = true;
+    document.body.appendChild(elem);
+    const eventPromises = [
+      "transitionrun",
+      "transitionstart",
+      "transitionend",
+    ].map(eventType => {
+      return new Promise(r => {
+        elem.addEventListener(eventType, r);
+      });
+    });
+    // Flushing style triggers transition.
+    getComputedStyle(elem).opacity;
+    elem.style.transition = "opacity .1s";
+    elem.style.opacity = 0;
+    getComputedStyle(elem).opacity;
+    // All the events fire...
+    await Promise.all(eventPromises);
+    elem.remove();
+  }
+}, "CSS Transitions transitionrun, transitionstart, transitionend events fire on disabled form elements");
+
+promise_test(async () => {
+  // For each form element type, set up transition event handlers.
+  for (const localName of formElements) {
+    const elem = document.createElement(localName);
+    elem.disabled = true;
+    document.body.appendChild(elem);
+    getComputedStyle(elem).opacity;
+    elem.style.transition = "opacity 100s";
+    // We use ontransitionstart to cancel the event.
+    elem.ontransitionstart = () => {
+      elem.style.display = "none";
+    };
+    const promiseToCancel = new Promise(r => {
+      elem.ontransitioncancel = r;
+    });
+    // Flushing style triggers the transition.
+    elem.style.opacity = 0;
+    getComputedStyle(elem).opacity;
+    await promiseToCancel;
+    // And we are done with this element.
+    elem.remove();
+  }
+}, "CSS Transitions transitioncancel event fires on disabled form elements");
+
+promise_test(async () => {
+  // For each form element type, set up transition event handlers.
+  for (const localName of formElements) {
+    const elem = document.createElement(localName);
+    document.body.appendChild(elem);
+    elem.disabled = true;
+    const animationStartPromise = new Promise(r => {
+      elem.addEventListener("animationstart", () => {
+        // Seek to the second iteration to trigger the animationiteration event
+        elem.style.animationDelay = "-100s"
+        r();
+      });
+    });
+    const animationIterationPromise = new Promise(r => {
+      elem.addEventListener("animationiteration", ()=>{
+        elem.style.animationDelay = "-200s"
+        r();
+      });
+    });
+    const animationEndPromise = new Promise(r => {
+      elem.addEventListener("animationend", r);
+    });
+    elem.style.animation = "fade 100s 2";
+    elem.classList.add("animate");
+    // All the events fire...
+    await Promise.all([
+      animationStartPromise,
+      animationIterationPromise,
+      animationEndPromise,
+    ]);
+    elem.remove();
+  }
+}, "CSS Animation animationstart, animationiteration, animationend fire on disabled form elements");
+
+promise_test(async () => {
+  // For each form element type, set up transition event handlers.
+  for (const localName of formElements) {
+    const elem = document.createElement(localName);
+    document.body.appendChild(elem);
+    elem.disabled = true;
+
+    const promiseToCancel = new Promise(r => {
+      elem.addEventListener("animationcancel", r);
+    });
+
+    elem.addEventListener("animationstart", () => {
+      // Cancel the animation by hiding it.
+      elem.style.display = "none";
+    });
+
+    // Trigger the animation
+    elem.style.animation = "fade 100s";
+    elem.classList.add("animate");
+    await promiseToCancel;
+    // And we are done with this element.
+    elem.remove();
+  }
+}, "CSS Animation's animationcancel event fires on disabled form elements");
+
+promise_test(async () => {
+  for (const localName of formElements) {
+    const elem = document.createElement(localName);
+    elem.disabled = true;
+    document.body.appendChild(elem);
+    // Element is disabled, so clicking must not fire events
+    let pass = true;
+    elem.onclick = e => {
+      pass = false;
+    };
+    // Disabled elements are not clickable.
+    await test_driver.click(elem);
+    assert_true(
+      pass,
+      `${elem.constructor.name} is disabled, so onclick must not fire.`
+    );
+    // Element is (re)enabled... so this click() will fire an event.
+    pass = false;
+    elem.disabled = false;
+    elem.onclick = () => {
+      pass = true;
+    };
+    await test_driver.click(elem);
+    assert_true(
+      pass,
+      `${elem.constructor.name} is enabled, so onclick must fire.`
+    );
+    elem.remove();
+  }
+}, "Real clicks on disabled elements must not dispatch events.");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-order-at-target.html b/testing/web-platform/tests/dom/events/Event-dispatch-order-at-target.html
new file mode 100644
index 0000000000..79673c3256
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-order-at-target.html
@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Listeners are invoked in correct order (AT_TARGET phase)</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+"use strict";
+
+test(() => {
+    const el = document.createElement("div");
+    const expectedOrder = ["capturing", "bubbling"];
+
+    let actualOrder = [];
+    el.addEventListener("click", evt => {
+        assert_equals(evt.eventPhase, Event.AT_TARGET);
+        actualOrder.push("bubbling");
+    }, false);
+    el.addEventListener("click", evt => {
+        assert_equals(evt.eventPhase, Event.AT_TARGET);
+        actualOrder.push("capturing");
+    }, true);
+
+    el.dispatchEvent(new Event("click", {bubbles: true}));
+    assert_array_equals(actualOrder, expectedOrder, "bubbles: true");
+
+    actualOrder = [];
+    el.dispatchEvent(new Event("click", {bubbles: false}));
+    assert_array_equals(actualOrder, expectedOrder, "bubbles: false");
+}, "Listeners are invoked in correct order (AT_TARGET phase)");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-order.html b/testing/web-platform/tests/dom/events/Event-dispatch-order.html
new file mode 100644
index 0000000000..ca94434595
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-order.html
@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<title>Event phases order</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+async_test(function() {
+    document.addEventListener('DOMContentLoaded', this.step_func_done(function() {
+        var parent = document.getElementById('parent');
+        var child = document.getElementById('child');
+
+        var order = [];
+
+        parent.addEventListener('click', this.step_func(function(){ order.push(1) }), true);
+        child.addEventListener('click', this.step_func(function(){ order.push(2) }), false);
+        parent.addEventListener('click', this.step_func(function(){ order.push(3) }), false);
+
+        child.dispatchEvent(new Event('click', {bubbles: true}));
+
+        assert_array_equals(order, [1, 2, 3]);
+    }));
+}, "Event phases order");
+</script>
+<div id="parent">
+    <div id="child"></div>
+</div>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-other-document.html b/testing/web-platform/tests/dom/events/Event-dispatch-other-document.html
new file mode 100644
index 0000000000..689b48087a
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-other-document.html
@@ -0,0 +1,23 @@
+<!doctype html>
+<title>Custom event on an element in another document</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id=log></div>
+<script>
+test(function() {
+  var doc = document.implementation.createHTMLDocument("Demo");
+  var element = doc.createElement("div");
+  var called = false;
+  element.addEventListener("foo", this.step_func(function(ev) {
+    assert_false(called);
+    called = true;
+    assert_equals(ev.target, element);
+    assert_equals(ev.srcElement, element);
+  }));
+  doc.body.appendChild(element);
+
+  var event = new Event("foo");
+  element.dispatchEvent(event);
+  assert_true(called);
+});
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-propagation-stopped.html b/testing/web-platform/tests/dom/events/Event-dispatch-propagation-stopped.html
new file mode 100644
index 0000000000..889f8cfe11
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-propagation-stopped.html
@@ -0,0 +1,59 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title> Calling stopPropagation() prior to dispatchEvent() </title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+<div id=log></div>
+
+<table id="table" border="1" style="display: none">
+    <tbody id="table-body">
+    <tr id="table-row">
+        <td id="table-cell">Shady Grove</td>
+        <td>Aeolian</td>
+    </tr>
+    <tr id="parent">
+        <td id="target">Over the river, Charlie</td>
+        <td>Dorian</td>
+    </tr>
+    </tbody>
+</table>
+
+<script>
+test(function() {
+    var event = "foo";
+    var target = document.getElementById("target");
+    var parent = document.getElementById("parent");
+    var tbody = document.getElementById("table-body");
+    var table = document.getElementById("table");
+    var body = document.body;
+    var html = document.documentElement;
+    var current_targets = [window, document, html, body, table, tbody, parent, target];
+    var expected_targets = [];
+    var actual_targets = [];
+    var expected_phases = [];
+    var actual_phases = [];
+
+    var test_event = function(evt) {
+        actual_targets.push(evt.currentTarget);
+        actual_phases.push(evt.eventPhase);
+    };
+
+    for (var i = 0; i < current_targets.length; ++i) {
+        current_targets[i].addEventListener(event, test_event, true);
+        current_targets[i].addEventListener(event, test_event, false);
+    }
+
+    var evt = document.createEvent("Event");
+    evt.initEvent(event, true, true);
+    evt.stopPropagation();
+    target.dispatchEvent(evt);
+
+    assert_array_equals(actual_targets, expected_targets, "actual_targets");
+    assert_array_equals(actual_phases, expected_phases, "actual_phases");
+});
+</script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-redispatch.html b/testing/web-platform/tests/dom/events/Event-dispatch-redispatch.html
new file mode 100644
index 0000000000..cf861ca177
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-redispatch.html
@@ -0,0 +1,124 @@
+<!DOCTYPE html>
+<meta charset=urf-8>
+<title>EventTarget#dispatchEvent(): redispatching a native event</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<button>click me!</button>
+<div id=log></div>
+<script>
+var test_contentLoaded_redispatching = async_test("Redispatching DOMContentLoaded event after being dispatched");
+var test_mouseup_redispatching = async_test("Redispatching mouseup event whose default action dispatches a click event");
+var test_redispatching_of_dispatching_event = async_test("Redispatching event which is being dispatched");
+
+var buttonElement = document.querySelector("button");
+var contentLoadedEvent;
+
+var waitForLoad = new Promise(resolve => {
+  window.addEventListener("load", () => { requestAnimationFrame(resolve); }, {capture: false, once: true});
+});
+
+document.addEventListener("DOMContentLoaded", event => {
+  contentLoadedEvent = event;
+  test_redispatching_of_dispatching_event.step(() => {
+    assert_throws_dom("InvalidStateError", () => {
+      document.dispatchEvent(contentLoadedEvent);
+    }, "Trusted DOMContentLoaded event");
+  });
+}, {capture: true, once: true});
+
+window.addEventListener("load", loadEvent => {
+  let untrustedContentLoadedEvent;
+  buttonElement.addEventListener("DOMContentLoaded", event => {
+    untrustedContentLoadedEvent = event;
+    test_contentLoaded_redispatching.step(() => {
+      assert_false(untrustedContentLoadedEvent.isTrusted, "Redispatched DOMContentLoaded event shouldn't be trusted");
+    });
+    test_redispatching_of_dispatching_event.step(() => {
+      assert_throws_dom("InvalidStateError", () => {
+        document.dispatchEvent(untrustedContentLoadedEvent);
+      }, "Untrusted DOMContentLoaded event");
+    });
+  });
+
+  test_contentLoaded_redispatching.step(() => {
+    assert_true(contentLoadedEvent.isTrusted, "Received DOMContentLoaded event should be trusted before redispatching");
+    buttonElement.dispatchEvent(contentLoadedEvent);
+    assert_false(contentLoadedEvent.isTrusted, "Received DOMContentLoaded event shouldn't be trusted after redispatching");
+    assert_not_equals(untrustedContentLoadedEvent, undefined, "Untrusted DOMContentLoaded event should've been fired");
+    test_contentLoaded_redispatching.done();
+  });
+}, {capture: true, once: true});
+
+async function testMouseUpAndClickEvent() {
+  let mouseupEvent;
+  buttonElement.addEventListener("mouseup", event => {
+    mouseupEvent = event;
+    test_mouseup_redispatching.step(() => {
+      assert_true(mouseupEvent.isTrusted, "First mouseup event should be trusted");
+    });
+    test_redispatching_of_dispatching_event.step(() => {
+      assert_throws_dom("InvalidStateError", () => {
+        buttonElement.dispatchEvent(mouseupEvent);
+      }, "Trusted mouseup event");
+    });
+  }, {once: true});
+
+  let clickEvent;
+  buttonElement.addEventListener("click", event => {
+    clickEvent = event;
+    test_mouseup_redispatching.step(() => {
+      assert_true(clickEvent.isTrusted, "First click event should be trusted");
+    });
+    test_redispatching_of_dispatching_event.step(() => {
+      assert_throws_dom("InvalidStateError", function() {
+        buttonElement.dispatchEvent(event);
+      }, "Trusted click event");
+    });
+    buttonElement.addEventListener("mouseup", event => {
+      test_mouseup_redispatching.step(() => {
+        assert_false(event.isTrusted, "Redispatched mouseup event shouldn't be trusted");
+      });
+      test_redispatching_of_dispatching_event.step(() => {
+        assert_throws_dom("InvalidStateError", function() {
+          buttonElement.dispatchEvent(event);
+        }, "Untrusted mouseup event");
+      });
+    }, {once: true});
+    function onClick() {
+      test_mouseup_redispatching.step(() => {
+        assert_true(false, "click event shouldn't be fired for dispatched mouseup event");
+      });
+    }
+    test_mouseup_redispatching.step(() => {
+      assert_true(mouseupEvent.isTrusted, "Received mouseup event should be trusted before redispatching from click event listener");
+      buttonElement.addEventListener("click", onClick);
+      buttonElement.dispatchEvent(mouseupEvent);
+      buttonElement.removeEventListener("click", onClick);
+      assert_false(mouseupEvent.isTrusted, "Received mouseup event shouldn't be trusted after redispatching");
+      assert_true(clickEvent.isTrusted, "First click event should still be trusted even after redispatching mouseup event");
+    });
+  }, {once: true});
+
+  await waitForLoad;
+  let bounds = buttonElement.getBoundingClientRect();
+  test(() => { assert_true(true); }, `Synthesizing click on button...`);
+  new test_driver.click(buttonElement)
+      .then(() => {
+        test_mouseup_redispatching.step(() => {
+          assert_not_equals(clickEvent, undefined, "mouseup and click events should've been fired");
+        });
+        test_mouseup_redispatching.done();
+        test_redispatching_of_dispatching_event.done();
+      }, (reason) => {
+        test_mouseup_redispatching.step(() => {
+          assert_true(false, `Failed to send mouse click due to ${reason}`);
+        });
+        test_mouseup_redispatching.done();
+        test_redispatching_of_dispatching_event.done();
+      });
+}
+testMouseUpAndClickEvent();
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-reenter.html b/testing/web-platform/tests/dom/events/Event-dispatch-reenter.html
new file mode 100644
index 0000000000..71f8517bdd
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-reenter.html
@@ -0,0 +1,66 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title> Dispatch additional events inside an event listener </title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id=log></div>
+<table id="table" border="1" style="display: none">
+    <tbody id="table-body">
+    <tr id="table-row">
+        <td id="table-cell">Shady Grove</td>
+        <td>Aeolian</td>
+    </tr>
+    <tr id="parent">
+        <td id="target">Over the river, Charlie</td>
+        <td>Dorian</td>
+    </tr>
+    </tbody>
+</table>
+<script>
+test(function() {
+    var event_type = "foo";
+    var target = document.getElementById("target");
+    var parent = document.getElementById("parent");
+    var tbody = document.getElementById("table-body");
+    var table = document.getElementById("table");
+    var body = document.body;
+    var html = document.documentElement;
+    var targets = [window, document, html, body, table, tbody, parent, target];
+    var expected_targets = [
+        window, document, html, body, table,
+        target, parent, tbody,
+        table, body, html, document, window,
+        tbody, parent, target];
+    var actual_targets = [];
+    var expected_types = [
+        "foo", "foo", "foo", "foo", "foo",
+        "bar", "bar", "bar",
+        "bar", "bar", "bar", "bar", "bar",
+        "foo", "foo", "foo"
+    ];
+
+    var actual_targets = [], actual_types = [];
+    var test_event = this.step_func(function(evt) {
+        actual_targets.push(evt.currentTarget);
+        actual_types.push(evt.type);
+
+        if (table == evt.currentTarget && event_type == evt.type) {
+            var e = document.createEvent("Event");
+            e.initEvent("bar", true, true);
+            target.dispatchEvent(e);
+        }
+    });
+
+    for (var i = 0; i < targets.length; ++i) {
+        targets[i].addEventListener(event_type, test_event, true);
+        targets[i].addEventListener("bar", test_event, false);
+    }
+
+    var evt = document.createEvent("Event");
+    evt.initEvent(event_type, false, true);
+    target.dispatchEvent(evt);
+
+    assert_array_equals(actual_targets, expected_targets, "actual_targets");
+    assert_array_equals(actual_types, expected_types, "actual_types");
+});
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-target-moved.html b/testing/web-platform/tests/dom/events/Event-dispatch-target-moved.html
new file mode 100644
index 0000000000..facb2c7b95
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-target-moved.html
@@ -0,0 +1,73 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title> Determined event propagation path - target moved </title>
+<link rel="help" href="https://dom.spec.whatwg.org/#concept-event-dispatch">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id=log></div>
+<table id="table" border="1" style="display: none">
+    <tbody id="table-body">
+    <tr id="table-row">
+        <td id="table-cell">Shady Grove</td>
+        <td>Aeolian</td>
+    </tr>
+    <tr id="parent">
+        <td id="target">Over the river, Charlie</td>
+        <td>Dorian</td>
+    </tr>
+    </tbody>
+</table>
+<script>
+test(function() {
+    var event_type = "foo";
+    var target = document.getElementById("target");
+    var parent = document.getElementById("parent");
+    var tbody = document.getElementById("table-body");
+    var table = document.getElementById("table");
+    var body = document.body;
+    var html = document.documentElement;
+    var targets = [window, document, html, body, table, tbody, parent, target];
+    var expected_targets = targets.concat([target, parent, tbody, table, body, html, document, window]);
+    var phases = [
+        Event.CAPTURING_PHASE,
+        Event.CAPTURING_PHASE,
+        Event.CAPTURING_PHASE,
+        Event.CAPTURING_PHASE,
+        Event.CAPTURING_PHASE,
+        Event.CAPTURING_PHASE,
+        Event.CAPTURING_PHASE,
+        Event.AT_TARGET,
+        Event.AT_TARGET,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+    ];
+
+    var actual_targets = [], actual_phases = [];
+    var test_event = this.step_func(function(evt) {
+        if (parent === target.parentNode) {
+            var table_row = document.getElementById("table-row");
+            table_row.appendChild(parent.removeChild(target));
+        }
+
+        actual_targets.push(evt.currentTarget);
+        actual_phases.push(evt.eventPhase);
+    });
+
+    for (var i = 0; i < targets.length; i++) {
+        targets[i].addEventListener(event_type, test_event, true);
+        targets[i].addEventListener(event_type, test_event, false);
+    }
+
+    var evt = document.createEvent("Event");
+    evt.initEvent(event_type, true, true);
+    target.dispatchEvent(evt);
+
+    assert_array_equals(actual_targets, expected_targets, "targets");
+    assert_array_equals(actual_phases, phases, "phases");
+}, "Event propagation path when an element in it is moved within the DOM");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-target-removed.html b/testing/web-platform/tests/dom/events/Event-dispatch-target-removed.html
new file mode 100644
index 0000000000..531799c3ad
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-target-removed.html
@@ -0,0 +1,72 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Determined event propagation path - target removed</title>
+<link rel="help" href="https://dom.spec.whatwg.org/#concept-event-dispatch">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id=log></div>
+<table id="table" border="1" style="display: none">
+    <tbody id="table-body">
+    <tr id="table-row">
+        <td id="table-cell">Shady Grove</td>
+        <td>Aeolian</td>
+    </tr>
+    <tr id="parent">
+        <td id="target">Over the river, Charlie</td>
+        <td>Dorian</td>
+    </tr>
+    </tbody>
+</table>
+<script>
+test(function() {
+    var event_type = "foo";
+    var target = document.getElementById("target");
+    var parent = document.getElementById("parent");
+    var tbody = document.getElementById("table-body");
+    var table = document.getElementById("table");
+    var body = document.body;
+    var html = document.documentElement;
+    var targets = [window, document, html, body, table, tbody, parent, target];
+    var expected_targets = targets.concat([target, parent, tbody, table, body, html, document, window]);
+    var phases = [
+        Event.CAPTURING_PHASE,
+        Event.CAPTURING_PHASE,
+        Event.CAPTURING_PHASE,
+        Event.CAPTURING_PHASE,
+        Event.CAPTURING_PHASE,
+        Event.CAPTURING_PHASE,
+        Event.CAPTURING_PHASE,
+        Event.AT_TARGET,
+        Event.AT_TARGET,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+        Event.BUBBLING_PHASE,
+    ];
+
+    var actual_targets = [], actual_phases = [];
+    var test_event = this.step_func(function(evt) {
+        if (parent === target.parentNode) {
+            parent.removeChild(target);
+        }
+
+        actual_targets.push(evt.currentTarget);
+        actual_phases.push(evt.eventPhase);
+    });
+
+    for (var i = 0; i < targets.length; i++) {
+        targets[i].addEventListener(event_type, test_event, true);
+        targets[i].addEventListener(event_type, test_event, false);
+    }
+
+    var evt = document.createEvent("Event");
+    evt.initEvent(event_type, true, true);
+    target.dispatchEvent(evt);
+
+    assert_array_equals(actual_targets, expected_targets, "targets");
+    assert_array_equals(actual_phases, phases, "phases");
+}, "Event propagation path when an element in it is removed from the DOM");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-dispatch-throwing.html b/testing/web-platform/tests/dom/events/Event-dispatch-throwing.html
new file mode 100644
index 0000000000..7d1c0d94a0
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-dispatch-throwing.html
@@ -0,0 +1,51 @@
+<!DOCTYPE html>
+<meta charset="UTF-8">
+<title>Throwing in event listeners</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+setup({allow_uncaught_exception:true})
+
+test(function() {
+    var errorEvents = 0;
+    window.onerror = this.step_func(function(e) {
+        assert_equals(typeof e, 'string');
+        ++errorEvents;
+    });
+
+    var element = document.createElement('div');
+
+    element.addEventListener('click', function() {
+        throw new Error('Error from only listener');
+    });
+
+    element.dispatchEvent(new Event('click'));
+
+    assert_equals(errorEvents, 1);
+}, "Throwing in event listener with a single listeners");
+
+test(function() {
+    var errorEvents = 0;
+    window.onerror = this.step_func(function(e) {
+        assert_equals(typeof e, 'string');
+        ++errorEvents;
+    });
+
+    var element = document.createElement('div');
+
+    var secondCalled = false;
+
+    element.addEventListener('click', function() {
+        throw new Error('Error from first listener');
+    });
+    element.addEventListener('click', this.step_func(function() {
+        secondCalled = true;
+    }), false);
+
+    element.dispatchEvent(new Event('click'));
+
+    assert_equals(errorEvents, 1);
+    assert_true(secondCalled);
+}, "Throwing in event listener with multiple listeners");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-init-while-dispatching.html b/testing/web-platform/tests/dom/events/Event-init-while-dispatching.html
new file mode 100644
index 0000000000..2aa1f6701c
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-init-while-dispatching.html
@@ -0,0 +1,83 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Re-initializing events while dispatching them</title>
+<link rel="author" title="Josh Matthews" href="mailto:josh@joshmatthews.net">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+var events = {
+  'KeyboardEvent': {
+    'constructor': function() { return new KeyboardEvent("type", {key: "A"}); },
+    'init': function(ev) { ev.initKeyboardEvent("type2", true, true, null, "a", 1, "", true, "") },
+    'check': function(ev) {
+       assert_equals(ev.key, "A", "initKeyboardEvent key setter should short-circuit");
+       assert_false(ev.repeat, "initKeyboardEvent repeat setter should short-circuit");
+       assert_equals(ev.location, 0, "initKeyboardEvent location setter should short-circuit");
+     }
+  },
+  'MouseEvent': {
+    'constructor': function() { return new MouseEvent("type"); },
+    'init': function(ev) { ev.initMouseEvent("type2", true, true, null, 0, 1, 1, 1, 1, true, true, true, true, 1, null) },
+    'check': function(ev) {
+      assert_equals(ev.screenX, 0, "initMouseEvent screenX setter should short-circuit");
+      assert_equals(ev.screenY, 0, "initMouseEvent screenY setter should short-circuit");
+      assert_equals(ev.clientX, 0, "initMouseEvent clientX setter should short-circuit");
+      assert_equals(ev.clientY, 0, "initMouseEvent clientY setter should short-circuit");
+      assert_false(ev.ctrlKey, "initMouseEvent ctrlKey setter should short-circuit");
+      assert_false(ev.altKey, "initMouseEvent altKey setter should short-circuit");
+      assert_false(ev.shiftKey, "initMouseEvent shiftKey setter should short-circuit");
+      assert_false(ev.metaKey, "initMouseEvent metaKey setter should short-circuit");
+      assert_equals(ev.button, 0, "initMouseEvent button setter should short-circuit");
+    }
+  },
+  'CustomEvent': {
+    'constructor': function() { return new CustomEvent("type") },
+    'init': function(ev) { ev.initCustomEvent("type2", true, true, 1) },
+    'check': function(ev) {
+      assert_equals(ev.detail, null, "initCustomEvent detail setter should short-circuit");
+    }
+  },
+  'UIEvent': {
+    'constructor': function() { return new UIEvent("type") },
+    'init': function(ev) { ev.initUIEvent("type2", true, true, window, 1) },
+    'check': function(ev) {
+      assert_equals(ev.view, null, "initUIEvent view setter should short-circuit");
+      assert_equals(ev.detail, 0, "initUIEvent detail setter should short-circuit");
+    }
+  },
+  'Event': {
+    'constructor': function() { return new Event("type") },
+    'init': function(ev) { ev.initEvent("type2", true, true) },
+    'check': function(ev) {
+      assert_equals(ev.bubbles, false, "initEvent bubbles setter should short-circuit");
+      assert_equals(ev.cancelable, false, "initEvent cancelable setter should short-circuit");
+      assert_equals(ev.type, "type", "initEvent type setter should short-circuit");
+    }
+  }
+};
+
+var names = Object.keys(events);
+for (var i = 0; i < names.length; i++) {
+  var t = async_test("Calling init" + names[i] + " while dispatching.");
+  t.step(function() {
+    var e = events[names[i]].constructor();
+
+    var target = document.createElement("div")
+    target.addEventListener("type", t.step_func(function() {
+      events[names[i]].init(e);
+
+      var o = e;
+      while ((o = Object.getPrototypeOf(o))) {
+        if (!(o.constructor.name in events)) {
+          break;
+        }
+        events[o.constructor.name].check(e);
+      }
+    }), false);
+
+    assert_equals(target.dispatchEvent(e), true, "dispatchEvent must return true")
+  });
+  t.done();
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-initEvent.html b/testing/web-platform/tests/dom/events/Event-initEvent.html
new file mode 100644
index 0000000000..ad1018d4da
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-initEvent.html
@@ -0,0 +1,136 @@
+<!DOCTYPE html>
+<title>Event.initEvent</title>
+<link rel="author" title="Ms2ger" href="mailto:Ms2ger@gmail.com">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+var booleans = [true, false];
+booleans.forEach(function(bubbles) {
+  booleans.forEach(function(cancelable) {
+    test(function() {
+      var e = document.createEvent("Event")
+      e.initEvent("type", bubbles, cancelable)
+
+      // Step 2.
+      // Stop (immediate) propagation flag is tested later
+      assert_equals(e.defaultPrevented, false, "defaultPrevented")
+      assert_equals(e.returnValue, true, "returnValue")
+      // Step 3.
+      assert_equals(e.isTrusted, false, "isTrusted")
+      // Step 4.
+      assert_equals(e.target, null, "target")
+      assert_equals(e.srcElement, null, "srcElement")
+      // Step 5.
+      assert_equals(e.type, "type", "type")
+      // Step 6.
+      assert_equals(e.bubbles, bubbles, "bubbles")
+      // Step 7.
+      assert_equals(e.cancelable, cancelable, "cancelable")
+    }, "Properties of initEvent(type, " + bubbles + ", " + cancelable + ")")
+  })
+})
+
+test(function() {
+  var e = document.createEvent("Event")
+  e.initEvent("type 1", true, false)
+  assert_equals(e.type, "type 1", "type (first init)")
+  assert_equals(e.bubbles, true, "bubbles (first init)")
+  assert_equals(e.cancelable, false, "cancelable (first init)")
+
+  e.initEvent("type 2", false, true)
+  assert_equals(e.type, "type 2", "type (second init)")
+  assert_equals(e.bubbles, false, "bubbles (second init)")
+  assert_equals(e.cancelable, true, "cancelable (second init)")
+}, "Calling initEvent multiple times (getting type).")
+
+test(function() {
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=998809
+  var e = document.createEvent("Event")
+  e.initEvent("type 1", true, false)
+  assert_equals(e.bubbles, true, "bubbles (first init)")
+  assert_equals(e.cancelable, false, "cancelable (first init)")
+
+  e.initEvent("type 2", false, true)
+  assert_equals(e.type, "type 2", "type (second init)")
+  assert_equals(e.bubbles, false, "bubbles (second init)")
+  assert_equals(e.cancelable, true, "cancelable (second init)")
+}, "Calling initEvent multiple times (not getting type).")
+
+// Step 2.
+async_test(function() {
+  // https://www.w3.org/Bugs/Public/show_bug.cgi?id=17715
+
+  var e = document.createEvent("Event")
+  e.initEvent("type", false, false)
+  assert_equals(e.type, "type", "type (first init)")
+  assert_equals(e.bubbles, false, "bubbles (first init)")
+  assert_equals(e.cancelable, false, "cancelable (first init)")
+
+  var target = document.createElement("div")
+  target.addEventListener("type", this.step_func(function() {
+    e.initEvent("fail", true, true)
+    assert_equals(e.type, "type", "type (second init)")
+    assert_equals(e.bubbles, false, "bubbles (second init)")
+    assert_equals(e.cancelable, false, "cancelable (second init)")
+  }), false)
+
+  assert_equals(target.dispatchEvent(e), true, "dispatchEvent must return true")
+
+  this.done()
+}, "Calling initEvent must not have an effect during dispatching.")
+
+test(function() {
+  var e = document.createEvent("Event")
+  e.stopPropagation()
+  e.initEvent("type", false, false)
+  var target = document.createElement("div")
+  var called = false
+  target.addEventListener("type", function() { called = true }, false)
+  assert_false(e.cancelBubble, "cancelBubble must be false")
+  assert_true(target.dispatchEvent(e), "dispatchEvent must return true")
+  assert_true(called, "Listener must be called")
+}, "Calling initEvent must unset the stop propagation flag.")
+
+test(function() {
+  var e = document.createEvent("Event")
+  e.stopImmediatePropagation()
+  e.initEvent("type", false, false)
+  var target = document.createElement("div")
+  var called = false
+  target.addEventListener("type", function() { called = true }, false)
+  assert_true(target.dispatchEvent(e), "dispatchEvent must return true")
+  assert_true(called, "Listener must be called")
+}, "Calling initEvent must unset the stop immediate propagation flag.")
+
+async_test(function() {
+  var e = document.createEvent("Event")
+  e.initEvent("type", false, false)
+
+  var target = document.createElement("div")
+  target.addEventListener("type", this.step_func(function() {
+    e.initEvent("type2", true, true);
+    assert_equals(e.type, "type", "initEvent type setter should short-circuit");
+    assert_false(e.bubbles, "initEvent bubbles setter should short-circuit");
+    assert_false(e.cancelable, "initEvent cancelable setter should short-circuit");
+  }), false)
+  assert_equals(target.dispatchEvent(e), true, "dispatchEvent must return true")
+
+  this.done()
+}, "Calling initEvent during propagation.")
+
+test(function() {
+  var e = document.createEvent("Event")
+  assert_throws_js(TypeError, function() {
+    e.initEvent()
+  })
+}, "First parameter to initEvent should be mandatory.")
+
+test(function() {
+  var e = document.createEvent("Event")
+  e.initEvent("type")
+  assert_equals(e.type, "type", "type")
+  assert_false(e.bubbles, "bubbles")
+  assert_false(e.cancelable, "cancelable")
+}, "Tests initEvent's default parameter values.")
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-isTrusted.any.js b/testing/web-platform/tests/dom/events/Event-isTrusted.any.js
new file mode 100644
index 0000000000..00bcecd0ed
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-isTrusted.any.js
@@ -0,0 +1,11 @@
+test(function() {
+  var desc1 = Object.getOwnPropertyDescriptor(new Event("x"), "isTrusted");
+  assert_not_equals(desc1, undefined);
+  assert_equals(typeof desc1.get, "function");
+
+  var desc2 = Object.getOwnPropertyDescriptor(new Event("x"), "isTrusted");
+  assert_not_equals(desc2, undefined);
+  assert_equals(typeof desc2.get, "function");
+
+  assert_equals(desc1.get, desc2.get);
+});
diff --git a/testing/web-platform/tests/dom/events/Event-propagation.html b/testing/web-platform/tests/dom/events/Event-propagation.html
new file mode 100644
index 0000000000..33989eb4bf
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-propagation.html
@@ -0,0 +1,48 @@
+<!doctype html>
+<title>Event propagation tests</title>
+<link rel=author title="Aryeh Gregor" href=ayg@aryeh.name>
+<div id=log></div>
+<script src=/resources/testharness.js></script>
+<script src=/resources/testharnessreport.js></script>
+<script>
+"use strict";
+
+function testPropagationFlag(ev, expected, desc) {
+  test(function() {
+    var called = false;
+    var callback = function() { called = true };
+    this.add_cleanup(function() {
+      document.head.removeEventListener("foo", callback)
+    });
+    document.head.addEventListener("foo", callback);
+    document.head.dispatchEvent(ev);
+    assert_equals(called, expected, "Propagation flag");
+    // dispatchEvent resets the propagation flags so it will happily dispatch
+    // the event the second time around.
+    document.head.dispatchEvent(ev);
+    assert_equals(called, true, "Propagation flag after first dispatch");
+  }, desc);
+}
+
+var ev = document.createEvent("Event");
+ev.initEvent("foo", true, false);
+testPropagationFlag(ev, true, "Newly-created Event");
+ev.stopPropagation();
+testPropagationFlag(ev, false, "After stopPropagation()");
+ev.initEvent("foo", true, false);
+testPropagationFlag(ev, true, "Reinitialized after stopPropagation()");
+
+var ev = document.createEvent("Event");
+ev.initEvent("foo", true, false);
+ev.stopImmediatePropagation();
+testPropagationFlag(ev, false, "After stopImmediatePropagation()");
+ev.initEvent("foo", true, false);
+testPropagationFlag(ev, true, "Reinitialized after stopImmediatePropagation()");
+
+var ev = document.createEvent("Event");
+ev.initEvent("foo", true, false);
+ev.cancelBubble = true;
+testPropagationFlag(ev, false, "After cancelBubble=true");
+ev.initEvent("foo", true, false);
+testPropagationFlag(ev, true, "Reinitialized after cancelBubble=true");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-returnValue.html b/testing/web-platform/tests/dom/events/Event-returnValue.html
new file mode 100644
index 0000000000..08df2d4141
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-returnValue.html
@@ -0,0 +1,64 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Event.returnValue</title>
+  <link rel="author" title="Chris Rebert" href="http://chrisrebert.com">
+  <link rel="help" href="https://dom.spec.whatwg.org/#dom-event-returnvalue">
+  <meta name="flags" content="dom">
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+  <div id="log"></div>
+  <script>
+test(function() {
+  var ev = new Event("foo");
+  assert_true(ev.returnValue, "returnValue");
+}, "When an event is created, returnValue should be initialized to true.");
+test(function() {
+  var ev = new Event("foo", {"cancelable": false});
+  assert_false(ev.cancelable, "cancelable (before)");
+  ev.preventDefault();
+  assert_false(ev.cancelable, "cancelable (after)");
+  assert_true(ev.returnValue, "returnValue");
+}, "preventDefault() should not change returnValue if cancelable is false.");
+test(function() {
+  var ev = new Event("foo", {"cancelable": false});
+  assert_false(ev.cancelable, "cancelable (before)");
+  ev.returnValue = false;
+  assert_false(ev.cancelable, "cancelable (after)");
+  assert_true(ev.returnValue, "returnValue");
+}, "returnValue=false should have no effect if cancelable is false.");
+test(function() {
+  var ev = new Event("foo", {"cancelable": true});
+  assert_true(ev.cancelable, "cancelable (before)");
+  ev.preventDefault();
+  assert_true(ev.cancelable, "cancelable (after)");
+  assert_false(ev.returnValue, "returnValue");
+}, "preventDefault() should change returnValue if cancelable is true.");
+test(function() {
+  var ev = new Event("foo", {"cancelable": true});
+  assert_true(ev.cancelable, "cancelable (before)");
+  ev.returnValue = false;
+  assert_true(ev.cancelable, "cancelable (after)");
+  assert_false(ev.returnValue, "returnValue");
+}, "returnValue should change returnValue if cancelable is true.");
+test(function() {
+  var ev = document.createEvent("Event");
+  ev.returnValue = false;
+  ev.initEvent("foo", true, true);
+  assert_true(ev.bubbles, "bubbles");
+  assert_true(ev.cancelable, "cancelable");
+  assert_true(ev.returnValue, "returnValue");
+}, "initEvent should unset returnValue.");
+test(function() {
+  var ev = new Event("foo", {"cancelable": true});
+  ev.preventDefault();
+  ev.returnValue = true;// no-op
+  assert_true(ev.defaultPrevented);
+  assert_false(ev.returnValue);
+}, "returnValue=true should have no effect once the canceled flag was set.");
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/dom/events/Event-stopImmediatePropagation.html b/testing/web-platform/tests/dom/events/Event-stopImmediatePropagation.html
new file mode 100644
index 0000000000..b75732257a
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-stopImmediatePropagation.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Event's stopImmediatePropagation</title>
+<link rel="help" href="https://dom.spec.whatwg.org/#dom-event-stopimmediatepropagation">
+<link rel="author" href="mailto:d@domenic.me" title="Domenic Denicola">
+
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<div id="target"></div>
+
+<script>
+"use strict";
+
+setup({ single_test: true });
+
+const target = document.querySelector("#target");
+
+let timesCalled = 0;
+target.addEventListener("test", e => {
+  ++timesCalled;
+  e.stopImmediatePropagation();
+  assert_equals(e.cancelBubble, true, "The stop propagation flag must have been set");
+});
+target.addEventListener("test", () => {
+  ++timesCalled;
+});
+
+const e = new Event("test");
+target.dispatchEvent(e);
+assert_equals(timesCalled, 1, "The second listener must not have been called");
+
+done();
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-stopPropagation-cancel-bubbling.html b/testing/web-platform/tests/dom/events/Event-stopPropagation-cancel-bubbling.html
new file mode 100644
index 0000000000..5c2c49f338
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-stopPropagation-cancel-bubbling.html
@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<link rel="author" title="Joey Arhar" href="mailto:jarhar@chromium.org">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<script>
+test(t => {
+  const element = document.createElement('div');
+
+  element.addEventListener('click', () => {
+    event.stopPropagation();
+  }, { capture: true });
+
+  element.addEventListener('click',
+    t.unreached_func('stopPropagation in the capture handler should have canceled this bubble handler.'));
+
+  element.dispatchEvent(new MouseEvent('click', { bubbles: true, cancelable: true }));
+});
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-subclasses-constructors.html b/testing/web-platform/tests/dom/events/Event-subclasses-constructors.html
new file mode 100644
index 0000000000..08a5ded011
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-subclasses-constructors.html
@@ -0,0 +1,179 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Event constructors</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+function assert_props(iface, event, defaults) {
+  assert_true(event instanceof self[iface]);
+  expected[iface].properties.forEach(function(p) {
+    var property = p[0], value = p[defaults ? 1 : 2];
+    assert_true(property in event,
+                "Event " + format_value(event) + " should have a " +
+                property + " property");
+    assert_equals(event[property], value,
+                  "The value of the " + property + " property should be " +
+                  format_value(value));
+  });
+  if ("parent" in expected[iface]) {
+    assert_props(expected[iface].parent, event, defaults);
+  }
+}
+
+// Class declarations don't go on the global by default, so put it there ourselves:
+
+self.SubclassedEvent = class SubclassedEvent extends Event {
+  constructor(name, props) {
+    super(name, props);
+    if (props && typeof(props) == "object" && "customProp" in props) {
+      this.customProp = props.customProp;
+    } else {
+      this.customProp = 5;
+    }
+  }
+
+  get fixedProp() {
+    return 17;
+  }
+}
+
+var EventModifierInit = [
+  ["ctrlKey", false, true],
+  ["shiftKey", false, true],
+  ["altKey", false, true],
+  ["metaKey", false, true],
+];
+var expected = {
+  "Event": {
+    "properties": [
+      ["bubbles", false, true],
+      ["cancelable", false, true],
+      ["isTrusted", false, false],
+    ],
+  },
+
+  "UIEvent": {
+    "parent": "Event",
+    "properties": [
+      ["view", null, window],
+      ["detail", 0, 7],
+    ],
+  },
+
+  "FocusEvent": {
+    "parent": "UIEvent",
+    "properties": [
+      ["relatedTarget", null, document],
+    ],
+  },
+
+  "MouseEvent": {
+    "parent": "UIEvent",
+    "properties": EventModifierInit.concat([
+      ["screenX", 0, 40],
+      ["screenY", 0, 40],
+      ["clientX", 0, 40],
+      ["clientY", 0, 40],
+      ["button", 0, 40],
+      ["buttons", 0, 40],
+      ["relatedTarget", null, document],
+    ]),
+  },
+
+  "WheelEvent": {
+    "parent": "MouseEvent",
+    "properties": [
+      ["deltaX", 0.0, 3.1],
+      ["deltaY", 0.0, 3.1],
+      ["deltaZ", 0.0, 3.1],
+      ["deltaMode", 0, 40],
+    ],
+  },
+
+  "KeyboardEvent": {
+    "parent": "UIEvent",
+    "properties": EventModifierInit.concat([
+      ["key", "", "string"],
+      ["code", "", "string"],
+      ["location", 0, 7],
+      ["repeat", false, true],
+      ["isComposing", false, true],
+      ["charCode", 0, 7],
+      ["keyCode", 0, 7],
+      ["which", 0, 7],
+    ]),
+  },
+
+  "CompositionEvent": {
+    "parent": "UIEvent",
+    "properties": [
+      ["data", "", "string"],
+    ],
+  },
+
+  "SubclassedEvent": {
+    "parent": "Event",
+    "properties": [
+      ["customProp", 5, 8],
+      ["fixedProp", 17, 17],
+    ],
+  },
+};
+
+Object.keys(expected).forEach(function(iface) {
+  test(function() {
+    var event = new self[iface]("type");
+    assert_props(iface, event, true);
+  }, iface + " constructor (no argument)");
+
+  test(function() {
+    var event = new self[iface]("type", undefined);
+    assert_props(iface, event, true);
+  }, iface + " constructor (undefined argument)");
+
+  test(function() {
+    var event = new self[iface]("type", null);
+    assert_props(iface, event, true);
+  }, iface + " constructor (null argument)");
+
+  test(function() {
+    var event = new self[iface]("type", {});
+    assert_props(iface, event, true);
+  }, iface + " constructor (empty argument)");
+
+  test(function() {
+    var dictionary = {};
+    expected[iface].properties.forEach(function(p) {
+      var property = p[0], value = p[1];
+      dictionary[property] = value;
+    });
+    var event = new self[iface]("type", dictionary);
+    assert_props(iface, event, true);
+  }, iface + " constructor (argument with default values)");
+
+  test(function() {
+    function fill_in(iface, dictionary) {
+      if ("parent" in expected[iface]) {
+        fill_in(expected[iface].parent, dictionary)
+      }
+      expected[iface].properties.forEach(function(p) {
+        var property = p[0], value = p[2];
+        dictionary[property] = value;
+      });
+    }
+
+    var dictionary = {};
+    fill_in(iface, dictionary);
+
+    var event = new self[iface]("type", dictionary);
+    assert_props(iface, event, false);
+  }, iface + " constructor (argument with non-default values)");
+});
+
+test(function () {
+  assert_throws_js(TypeError, function() {
+    new UIEvent("x", { view: 7 })
+  });
+}, "UIEvent constructor (view argument with wrong type)")
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-timestamp-cross-realm-getter.html b/testing/web-platform/tests/dom/events/Event-timestamp-cross-realm-getter.html
new file mode 100644
index 0000000000..45823de26b
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-timestamp-cross-realm-getter.html
@@ -0,0 +1,27 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>event.timeStamp is initialized using event's relevant global object</title>
+<link rel="help" href="https://dom.spec.whatwg.org/#ref-for-dom-event-timestamp%E2%91%A1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body>
+<script>
+const t = async_test();
+t.step_timeout(() => {
+  const iframeDelayed = document.createElement("iframe");
+  iframeDelayed.onload = t.step_func_done(() => {
+    // Use eval() to eliminate false-positive test result for WebKit builds before r280256,
+    // which invoked WebIDL accessors in context of lexical (caller) global object.
+    const timeStampExpected = iframeDelayed.contentWindow.eval(`new Event("foo").timeStamp`);
+    const eventDelayed = new iframeDelayed.contentWindow.Event("foo");
+
+    const {get} = Object.getOwnPropertyDescriptor(Event.prototype, "timeStamp");
+    assert_approx_equals(get.call(eventDelayed), timeStampExpected, 5, "via Object.getOwnPropertyDescriptor");
+
+    Object.setPrototypeOf(eventDelayed, Event.prototype);
+    assert_approx_equals(eventDelayed.timeStamp, timeStampExpected, 5, "via Object.setPrototypeOf");
+  });
+  document.body.append(iframeDelayed);
+}, 1000);
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-timestamp-high-resolution.html b/testing/web-platform/tests/dom/events/Event-timestamp-high-resolution.html
new file mode 100644
index 0000000000..a049fef64b
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-timestamp-high-resolution.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script type="text/javascript">
+'use strict';
+for (let eventType of ["MouseEvent", "KeyboardEvent", "WheelEvent", "FocusEvent"]) {
+    test(function() {
+        let before = performance.now();
+        let e = new window[eventType]('test');
+        let after = performance.now();
+        assert_greater_than_equal(e.timeStamp, before, "Event timestamp should be greater than performance.now() timestamp taken before its creation");
+        assert_less_than_equal(e.timeStamp, after, "Event timestamp should be less than performance.now() timestamp taken after its creation");
+    }, `Constructed ${eventType} timestamp should be high resolution and have the same time origin as performance.now()`);
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-timestamp-high-resolution.https.html b/testing/web-platform/tests/dom/events/Event-timestamp-high-resolution.https.html
new file mode 100644
index 0000000000..70f9742947
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-timestamp-high-resolution.https.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script type="text/javascript">
+'use strict';
+for (let eventType of ["GamepadEvent"]) {
+    test(function() {
+        let before = performance.now();
+        let e = new window[eventType]('test');
+        let after = performance.now();
+        assert_greater_than_equal(e.timeStamp, before, "Event timestamp should be greater than performance.now() timestamp taken before its creation");
+        assert_less_than_equal(e.timeStamp, after, "Event timestamp should be less than performance.now() timestamp taken after its creation");
+    }, `Constructed ${eventType} timestamp should be high resolution and have the same time origin as performance.now()`);
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-timestamp-safe-resolution.html b/testing/web-platform/tests/dom/events/Event-timestamp-safe-resolution.html
new file mode 100644
index 0000000000..24f2dec93c
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-timestamp-safe-resolution.html
@@ -0,0 +1,49 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script type="text/javascript">
+'use strict';
+
+// Computes greatest common divisor of a and b using Euclid's algorithm
+function computeGCD(a, b) {
+  if (!Number.isInteger(a) || !Number.isInteger(b)) {
+    throw new Error('Parameters must be integer numbers');
+  }
+
+  var r;
+  while (b != 0) {
+    r = a % b;
+    a = b;
+    b = r;
+  }
+  return (a < 0) ? -a : a;
+}
+
+// Finds minimum resolution Δ given a set of samples which are known to be in the form of N*Δ.
+// We use GCD of all samples as a simple estimator.
+function estimateMinimumResolution(samples) {
+  var gcd;
+  for (const sample of samples) {
+    gcd = gcd ? computeGCD(gcd, sample) : sample;
+  }
+
+  return gcd;
+}
+
+test(function() {
+  const samples = [];
+  for (var i = 0; i < 1e3; i++) {
+    var deltaInMicroSeconds = 0;
+    const e1 = new MouseEvent('test1');
+    do {
+      const e2 = new MouseEvent('test2');
+      deltaInMicroSeconds = Math.round((e2.timeStamp - e1.timeStamp) * 1000);
+    } while (deltaInMicroSeconds == 0) // only collect non-zero samples
+
+    samples.push(deltaInMicroSeconds);
+  }
+
+  const minResolution = estimateMinimumResolution(samples);
+  assert_greater_than_equal(minResolution, 5);
+}, 'Event timestamp should not have a resolution better than 5 microseconds');
+</script>
\ No newline at end of file
diff --git a/testing/web-platform/tests/dom/events/Event-type-empty.html b/testing/web-platform/tests/dom/events/Event-type-empty.html
new file mode 100644
index 0000000000..225b85a613
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-type-empty.html
@@ -0,0 +1,35 @@
+<!DOCTYPE html>
+<title>Event.type set to the empty string</title>
+<link rel="author" title="Ms2ger" href="mailto:Ms2ger@gmail.com">
+<link rel="help" href="https://dom.spec.whatwg.org/#dom-event-type">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+function do_test(t, e) {
+  assert_equals(e.type, "", "type");
+  assert_equals(e.bubbles, false, "bubbles");
+  assert_equals(e.cancelable, false, "cancelable");
+
+  var target = document.createElement("div");
+  var handled = false;
+  target.addEventListener("", t.step_func(function(e) {
+    handled = true;
+  }));
+  assert_true(target.dispatchEvent(e));
+  assert_true(handled);
+}
+
+async_test(function() {
+  var e = document.createEvent("Event");
+  e.initEvent("", false, false);
+  do_test(this, e);
+  this.done();
+}, "initEvent");
+
+async_test(function() {
+  var e = new Event("");
+  do_test(this, e);
+  this.done();
+}, "Constructor");
+</script>
diff --git a/testing/web-platform/tests/dom/events/Event-type.html b/testing/web-platform/tests/dom/events/Event-type.html
new file mode 100644
index 0000000000..22792f5c6c
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/Event-type.html
@@ -0,0 +1,22 @@
+<!DOCTYPE html>
+<title>Event.type</title>
+<link rel="author" title="Ms2ger" href="mailto:Ms2ger@gmail.com">
+<link rel="help" href="https://dom.spec.whatwg.org/#dom-event-type">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+test(function() {
+  var e = document.createEvent("Event")
+  assert_equals(e.type, "");
+}, "Event.type should initially be the empty string");
+test(function() {
+  var e = document.createEvent("Event")
+  e.initEvent("foo", false, false)
+  assert_equals(e.type, "foo")
+}, "Event.type should be initialized by initEvent");
+test(function() {
+  var e = new Event("bar")
+  assert_equals(e.type, "bar")
+}, "Event.type should be initialized by the constructor");
+</script>
diff --git a/testing/web-platform/tests/dom/events/EventListener-addEventListener.sub.window.js b/testing/web-platform/tests/dom/events/EventListener-addEventListener.sub.window.js
new file mode 100644
index 0000000000..b44bc33285
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventListener-addEventListener.sub.window.js
@@ -0,0 +1,9 @@
+async_test(function(t) {
+  let crossOriginFrame = document.createElement('iframe');
+  crossOriginFrame.src = 'https://{{hosts[alt][]}}:{{ports[https][0]}}/common/blank.html';
+  document.body.appendChild(crossOriginFrame);
+  crossOriginFrame.addEventListener('load', t.step_func_done(function() {
+    let crossOriginWindow = crossOriginFrame.contentWindow;
+    window.addEventListener('click', crossOriginWindow);
+  }));
+}, "EventListener.addEventListener doesn't throw when a cross origin object is passed in.");
diff --git a/testing/web-platform/tests/dom/events/EventListener-handleEvent-cross-realm.html b/testing/web-platform/tests/dom/events/EventListener-handleEvent-cross-realm.html
new file mode 100644
index 0000000000..663d04213f
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventListener-handleEvent-cross-realm.html
@@ -0,0 +1,75 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Cross-realm EventListener throws TypeError of its associated Realm</title>
+<link rel="help" href="https://webidl.spec.whatwg.org/#ref-for-prepare-to-run-script">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<iframe name="eventListenerGlobalObject" src="resources/empty-document.html"></iframe>
+
+<script>
+setup({ allow_uncaught_exception: true });
+
+test_onload(() => {
+    const eventTarget = new EventTarget;
+    const eventListener = new eventListenerGlobalObject.Object;
+
+    eventTarget.addEventListener("foo", eventListener);
+    assert_reports_exception(eventListenerGlobalObject.TypeError, () => { eventTarget.dispatchEvent(new Event("foo")); });
+}, "EventListener is cross-realm plain object without 'handleEvent' property");
+
+test_onload(() => {
+    const eventTarget = new EventTarget;
+    const eventListener = new eventListenerGlobalObject.Object;
+    eventListener.handleEvent = {};
+
+    eventTarget.addEventListener("foo", eventListener);
+    assert_reports_exception(eventListenerGlobalObject.TypeError, () => { eventTarget.dispatchEvent(new Event("foo")); });
+}, "EventListener is cross-realm plain object with non-callable 'handleEvent' property");
+
+test_onload(() => {
+    const eventTarget = new EventTarget;
+    const { proxy, revoke } = Proxy.revocable(() => {}, {});
+    revoke();
+
+    const eventListener = new eventListenerGlobalObject.Object;
+    eventListener.handleEvent = proxy;
+
+    eventTarget.addEventListener("foo", eventListener);
+    assert_reports_exception(eventListenerGlobalObject.TypeError, () => { eventTarget.dispatchEvent(new Event("foo")); });
+}, "EventListener is cross-realm plain object with revoked Proxy as 'handleEvent' property");
+
+test_onload(() => {
+    const eventTarget = new EventTarget;
+    const { proxy, revoke } = eventListenerGlobalObject.Proxy.revocable({}, {});
+    revoke();
+
+    eventTarget.addEventListener("foo", proxy);
+    assert_reports_exception(eventListenerGlobalObject.TypeError, () => { eventTarget.dispatchEvent(new Event("foo")); });
+}, "EventListener is cross-realm non-callable revoked Proxy");
+
+test_onload(() => {
+    const eventTarget = new EventTarget;
+    const { proxy, revoke } = eventListenerGlobalObject.Proxy.revocable(() => {}, {});
+    revoke();
+
+    eventTarget.addEventListener("foo", proxy);
+    assert_reports_exception(eventListenerGlobalObject.TypeError, () => { eventTarget.dispatchEvent(new Event("foo")); });
+}, "EventListener is cross-realm callable revoked Proxy");
+
+function test_onload(fn, desc) {
+    async_test(t => { window.addEventListener("load", t.step_func_done(fn)); }, desc);
+}
+
+function assert_reports_exception(expectedConstructor, fn) {
+    let error;
+    const onErrorHandler = event => { error = event.error; };
+
+    eventListenerGlobalObject.addEventListener("error", onErrorHandler);
+    fn();
+    eventListenerGlobalObject.removeEventListener("error", onErrorHandler);
+
+    assert_equals(typeof error, "object");
+    assert_equals(error.constructor, expectedConstructor);
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/EventListener-handleEvent.html b/testing/web-platform/tests/dom/events/EventListener-handleEvent.html
new file mode 100644
index 0000000000..06bc1f6e2a
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventListener-handleEvent.html
@@ -0,0 +1,102 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>EventListener::handleEvent()</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<link rel="help" href="https://dom.spec.whatwg.org/#callbackdef-eventlistener">
+<div id=log></div>
+<script>
+setup({ allow_uncaught_exception: true });
+
+test(function(t) {
+    var type = "foo";
+    var target = document.createElement("div");
+    var eventListener = {
+        handleEvent: function(evt) {
+            var that = this;
+            t.step(function() {
+                assert_equals(evt.type, type);
+                assert_equals(evt.target, target);
+                assert_equals(evt.srcElement, target);
+                assert_equals(that, eventListener);
+            });
+        },
+    };
+
+    target.addEventListener(type, eventListener);
+    target.dispatchEvent(new Event(type));
+}, "calls `handleEvent` method of `EventListener`");
+
+test(function(t) {
+    var type = "foo";
+    var target = document.createElement("div");
+    var calls = 0;
+
+    target.addEventListener(type, {
+        get handleEvent() {
+            calls++;
+            return function() {};
+        },
+    });
+
+    assert_equals(calls, 0);
+    target.dispatchEvent(new Event(type));
+    target.dispatchEvent(new Event(type));
+    assert_equals(calls, 2);
+}, "performs `Get` every time event is dispatched");
+
+test(function(t) {
+    var type = "foo";
+    var target = document.createElement("div");
+    var calls = 0;
+    var eventListener = function() { calls++; };
+    eventListener.handleEvent = t.unreached_func("`handleEvent` method should not be called on functions");
+
+    target.addEventListener(type, eventListener);
+    target.dispatchEvent(new Event(type));
+    assert_equals(calls, 1);
+}, "doesn't call `handleEvent` method on callable `EventListener`");
+
+const uncaught_error_test = async (t, getHandleEvent) => {
+    const type = "foo";
+    const target = document.createElement("div");
+
+    let calls = 0;
+    target.addEventListener(type, {
+        get handleEvent() {
+            calls++;
+            return getHandleEvent();
+        },
+    });
+
+    const timeout = () => {
+        return new Promise(resolve => {
+            t.step_timeout(resolve, 0);
+        });
+    };
+
+    const eventWatcher = new EventWatcher(t, window, "error", timeout);
+    const errorPromise = eventWatcher.wait_for("error");
+
+    target.dispatchEvent(new Event(type));
+
+    const event = await errorPromise;
+    assert_equals(calls, 1, "handleEvent property was not looked up");
+    throw event.error;
+};
+
+promise_test(t => {
+    const error = { name: "test" };
+
+    return promise_rejects_exactly(t, error,
+        uncaught_error_test(t, () => { throw error; }));
+}, "rethrows errors when getting `handleEvent`");
+
+promise_test(t => {
+    return promise_rejects_js(t, TypeError, uncaught_error_test(t, () => null));
+}, "throws if `handleEvent` is falsy and not callable");
+
+promise_test(t => {
+    return promise_rejects_js(t, TypeError, uncaught_error_test(t, () => 42));
+}, "throws if `handleEvent` is thruthy and not callable");
+</script>
diff --git a/testing/web-platform/tests/dom/events/EventListener-incumbent-global-1.sub.html b/testing/web-platform/tests/dom/events/EventListener-incumbent-global-1.sub.html
new file mode 100644
index 0000000000..9d941385cb
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventListener-incumbent-global-1.sub.html
@@ -0,0 +1,20 @@
+<!doctype html>
+<meta charset=utf-8>
+<title></title>
+<script src=/resources/testharness.js></script>
+<script src=/resources/testharnessreport.js></script>
+<iframe src="{{location[scheme]}}://{{domains[www1]}}:{{ports[http][0]}}{{location[path]}}/../EventListener-incumbent-global-subframe-1.sub.html"></iframe>
+<script>
+
+var t = async_test("Check the incumbent global EventListeners  are called with");
+
+onload = t.step_func(function() {
+  onmessage = t.step_func_done(function(e) {
+    var d = e.data;
+    assert_equals(d.actual, d.expected, d.reason);
+  });
+
+  frames[0].postMessage("start", "*");
+});
+
+</script>
diff --git a/testing/web-platform/tests/dom/events/EventListener-incumbent-global-2.sub.html b/testing/web-platform/tests/dom/events/EventListener-incumbent-global-2.sub.html
new file mode 100644
index 0000000000..4433c098d7
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventListener-incumbent-global-2.sub.html
@@ -0,0 +1,20 @@
+<!doctype html>
+<meta charset=utf-8>
+<title></title>
+<script src=/resources/testharness.js></script>
+<script src=/resources/testharnessreport.js></script>
+<iframe src="{{location[scheme]}}://{{domains[www1]}}:{{ports[http][0]}}{{location[path]}}/../EventListener-incumbent-global-subframe-2.sub.html"></iframe>
+<script>
+
+var t = async_test("Check the incumbent global EventListeners  are called with");
+
+onload = t.step_func(function() {
+  onmessage = t.step_func_done(function(e) {
+    var d = e.data;
+    assert_equals(d.actual, d.expected, d.reason);
+  });
+
+  frames[0].postMessage("start", "*");
+});
+
+</script>
diff --git a/testing/web-platform/tests/dom/events/EventListener-incumbent-global-subframe-1.sub.html b/testing/web-platform/tests/dom/events/EventListener-incumbent-global-subframe-1.sub.html
new file mode 100644
index 0000000000..25487cc5e0
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventListener-incumbent-global-subframe-1.sub.html
@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<iframe src="{{location[scheme]}}://{{domains[www2]}}:{{ports[http][0]}}{{location[path]}}/../EventListener-incumbent-global-subsubframe.sub.html"></iframe>
+<script>
+  document.domain = "{{host}}";
+  onmessage = function(e) {
+    if (e.data == "start") {
+      frames[0].document.body.addEventListener("click", frames[0].postMessage.bind(frames[0], "respond", "*", undefined));
+      frames[0].postMessage("sendclick", "*");
+    } else {
+      parent.postMessage(e.data, "*");
+    }
+  }
+</script>
diff --git a/testing/web-platform/tests/dom/events/EventListener-incumbent-global-subframe-2.sub.html b/testing/web-platform/tests/dom/events/EventListener-incumbent-global-subframe-2.sub.html
new file mode 100644
index 0000000000..9c7235e2ad
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventListener-incumbent-global-subframe-2.sub.html
@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<iframe src="{{location[scheme]}}://{{domains[www2]}}:{{ports[http][0]}}{{location[path]}}/../EventListener-incumbent-global-subsubframe.sub.html"></iframe>
+<script>
+  document.domain = "{{host}}";
+  onmessage = function(e) {
+    if (e.data == "start") {
+      frames[0].document.body.addEventListener("click", frames[0].getTheListener());
+      frames[0].postMessage("sendclick", "*");
+    } else {
+      parent.postMessage(e.data, "*");
+    }
+  }
+</script>
diff --git a/testing/web-platform/tests/dom/events/EventListener-incumbent-global-subsubframe.sub.html b/testing/web-platform/tests/dom/events/EventListener-incumbent-global-subsubframe.sub.html
new file mode 100644
index 0000000000..dd683f6f65
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventListener-incumbent-global-subsubframe.sub.html
@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+<script>
+  function getTheListener() {
+    return postMessage.bind(this, "respond", "*", undefined)
+  }
+  document.domain = "{{host}}";
+  onmessage = function (e) {
+    if (e.data == "sendclick") {
+      document.body.click();
+    } else {
+      parent.postMessage(
+        {
+          actual: e.origin,
+          expected: parent.location.origin,
+          reason: "Incumbent should have been the caller of addEventListener()"
+        },
+        "*")
+    };
+  }
+</script>
diff --git a/testing/web-platform/tests/dom/events/EventListener-invoke-legacy.html b/testing/web-platform/tests/dom/events/EventListener-invoke-legacy.html
new file mode 100644
index 0000000000..a01afcd8d1
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventListener-invoke-legacy.html
@@ -0,0 +1,66 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Invoke legacy event listener</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+  @keyframes test {
+    0% { color: red; }
+    100% { color: green; }
+  }
+</style>
+<div id="log"></div>
+<script>
+function runLegacyEventTest(type, legacyType, ctor, setup) {
+  function createTestElem(t) {
+    var elem = document.createElement('div');
+    document.body.appendChild(elem);
+    t.add_cleanup(function() {
+      document.body.removeChild(elem);
+    });
+    return elem;
+  }
+
+  async_test(function(t) {
+    var elem = createTestElem(t);
+    var gotEvent = false;
+    elem.addEventListener(legacyType,
+      t.unreached_func("listener of " + legacyType + " should not be invoked"));
+    elem.addEventListener(type, t.step_func(function() {
+      assert_false(gotEvent, "unexpected " + type + " event");
+      gotEvent = true;
+      t.step_timeout(function() { t.done(); }, 100);
+    }));
+    setup(elem);
+  }, "Listener of " + type);
+
+  async_test(function(t) {
+    var elem = createTestElem(t);
+    var count = 0;
+    elem.addEventListener(legacyType, t.step_func(function() {
+      ++count;
+      if (count > 1) {
+        assert_unreached("listener of " + legacyType + " should not be invoked again");
+        return;
+      }
+      elem.dispatchEvent(new window[ctor](type));
+      t.done();
+    }));
+    setup(elem);
+  }, "Legacy listener of " + type);
+}
+
+function setupTransition(elem) {
+  getComputedStyle(elem).color;
+  elem.style.color = 'green';
+  elem.style.transition = 'color 30ms';
+}
+
+function setupAnimation(elem) {
+  elem.style.animation = 'test 30ms';
+}
+
+runLegacyEventTest('transitionend', 'webkitTransitionEnd', "TransitionEvent", setupTransition);
+runLegacyEventTest('animationend', 'webkitAnimationEnd', "AnimationEvent", setupAnimation);
+runLegacyEventTest('animationstart', 'webkitAnimationStart', "AnimationEvent", setupAnimation);
+</script>
diff --git a/testing/web-platform/tests/dom/events/EventListenerOptions-capture.html b/testing/web-platform/tests/dom/events/EventListenerOptions-capture.html
new file mode 100644
index 0000000000..f72cf3ca54
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventListenerOptions-capture.html
@@ -0,0 +1,98 @@
+<!DOCTYPE HTML>
+<meta charset="utf-8">
+<title>EventListenerOptions.capture</title>
+<link rel="author" title="Rick Byers" href="mailto:rbyers@chromium.org">
+<link rel="help" href="https://dom.spec.whatwg.org/#dom-eventlisteneroptions-capture">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+
+<script>
+
+function testCaptureValue(captureValue, expectedValue) {
+  var handlerPhase = undefined;
+  var handler = function handler(e) {
+    assert_equals(handlerPhase, undefined, "Handler invoked after remove");
+    handlerPhase = e.eventPhase;
+  }
+  document.addEventListener('test', handler, captureValue);
+  document.body.dispatchEvent(new Event('test', {bubbles: true}));
+  document.removeEventListener('test', handler, captureValue);
+  document.body.dispatchEvent(new Event('test', {bubbles: true}));
+  assert_equals(handlerPhase, expectedValue, "Incorrect event phase for value: " + JSON.stringify(captureValue));
+}
+
+test(function() {
+  testCaptureValue(true, Event.CAPTURING_PHASE);
+  testCaptureValue(false, Event.BUBBLING_PHASE);
+  testCaptureValue(null, Event.BUBBLING_PHASE);
+  testCaptureValue(undefined, Event.BUBBLING_PHASE);
+  testCaptureValue(2.3, Event.CAPTURING_PHASE);
+  testCaptureValue(-1000.3, Event.CAPTURING_PHASE);
+  testCaptureValue(NaN, Event.BUBBLING_PHASE);
+  testCaptureValue(+0.0, Event.BUBBLING_PHASE);
+  testCaptureValue(-0.0, Event.BUBBLING_PHASE);
+  testCaptureValue("", Event.BUBBLING_PHASE);
+  testCaptureValue("AAAA", Event.CAPTURING_PHASE);
+}, "Capture boolean should be honored correctly");
+
+test(function() {
+  testCaptureValue({}, Event.BUBBLING_PHASE);
+  testCaptureValue({capture:true}, Event.CAPTURING_PHASE);
+  testCaptureValue({capture:false}, Event.BUBBLING_PHASE);
+  testCaptureValue({capture:2}, Event.CAPTURING_PHASE);
+  testCaptureValue({capture:0}, Event.BUBBLING_PHASE);
+}, "Capture option should be honored correctly");
+
+test(function() {
+  var supportsCapture = false;
+  var query_options = {
+    get capture() {
+      supportsCapture = true;
+      return false;
+    },
+    get dummy() {
+      assert_unreached("dummy value getter invoked");
+      return false;
+    }
+  };
+
+  document.addEventListener('test_event', null, query_options);
+  assert_true(supportsCapture, "addEventListener doesn't support the capture option");
+  supportsCapture = false;
+  document.removeEventListener('test_event', null, query_options);
+  assert_true(supportsCapture, "removeEventListener doesn't support the capture option");
+}, "Supports capture option");
+
+function testOptionEquality(addOptionValue, removeOptionValue, expectedEquality) {
+  var handlerInvoked = false;
+  var handler = function handler(e) {
+    assert_equals(handlerInvoked, false, "Handler invoked multiple times");
+    handlerInvoked = true;
+  }
+  document.addEventListener('test', handler, addOptionValue);
+  document.removeEventListener('test', handler, removeOptionValue);
+  document.body.dispatchEvent(new Event('test', {bubbles: true}));
+  assert_equals(!handlerInvoked, expectedEquality, "equivalence of options " +
+    JSON.stringify(addOptionValue) + " and " + JSON.stringify(removeOptionValue));
+  if (handlerInvoked)
+    document.removeEventListener('test', handler, addOptionValue);
+}
+
+test(function() {
+  // Option values that should be treated as equivalent
+  testOptionEquality({}, false, true);
+  testOptionEquality({capture: false}, false, true);
+  testOptionEquality(true, {capture: true}, true);
+  testOptionEquality({capture: null}, undefined, true);
+  testOptionEquality({capture: true}, {dummy: false, capture: 1}, true);
+  testOptionEquality({dummy: true}, false, true);
+
+  // Option values that should be treated as distinct
+  testOptionEquality(true, false, false);
+  testOptionEquality(true, {capture:false}, false);
+  testOptionEquality({}, true, false);
+
+}, "Equivalence of option values");
+
+</script>
diff --git a/testing/web-platform/tests/dom/events/EventTarget-add-listener-platform-object.html b/testing/web-platform/tests/dom/events/EventTarget-add-listener-platform-object.html
new file mode 100644
index 0000000000..d5565c22b3
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventTarget-add-listener-platform-object.html
@@ -0,0 +1,32 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>addEventListener with a platform object</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+</script>
+<my-custom-click id=click>Click me!</my-custom-click>
+<script>
+"use strict";
+setup({ single_test: true });
+
+class MyCustomClick extends HTMLElement {
+  connectedCallback() {
+    this.addEventListener("click", this);
+  }
+
+  handleEvent(event) {
+    if (event.target === this) {
+      this.dataset.yay = "It worked!";
+    }
+  }
+}
+window.customElements.define("my-custom-click", MyCustomClick);
+
+const customElement = document.getElementById("click");
+customElement.click();
+
+assert_equals(customElement.dataset.yay, "It worked!");
+
+done();
+</script>
diff --git a/testing/web-platform/tests/dom/events/EventTarget-add-remove-listener.any.js b/testing/web-platform/tests/dom/events/EventTarget-add-remove-listener.any.js
new file mode 100644
index 0000000000..b1d7ffb3e0
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventTarget-add-remove-listener.any.js
@@ -0,0 +1,21 @@
+// META: title=EventTarget's addEventListener + removeEventListener
+
+"use strict";
+
+function listener(evt) {
+  evt.preventDefault();
+  return false;
+}
+
+test(() => {
+  const et = new EventTarget();
+  et.addEventListener("x", listener, false);
+  let event = new Event("x", { cancelable: true });
+  let ret = et.dispatchEvent(event);
+  assert_false(ret);
+
+  et.removeEventListener("x", listener);
+  event = new Event("x", { cancelable: true });
+  ret = et.dispatchEvent(event);
+  assert_true(ret);
+}, "Removing an event listener without explicit capture arg should succeed");
diff --git a/testing/web-platform/tests/dom/events/EventTarget-addEventListener.any.js b/testing/web-platform/tests/dom/events/EventTarget-addEventListener.any.js
new file mode 100644
index 0000000000..e22da4aff8
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventTarget-addEventListener.any.js
@@ -0,0 +1,9 @@
+// META: title=EventTarget.addEventListener
+
+// Step 1.
+test(function() {
+  const et = new EventTarget();
+  assert_equals(et.addEventListener("x", null, false), undefined);
+  assert_equals(et.addEventListener("x", null, true), undefined);
+  assert_equals(et.addEventListener("x", null), undefined);
+}, "Adding a null event listener should succeed");
diff --git a/testing/web-platform/tests/dom/events/EventTarget-constructible.any.js b/testing/web-platform/tests/dom/events/EventTarget-constructible.any.js
new file mode 100644
index 0000000000..b0e7614e62
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventTarget-constructible.any.js
@@ -0,0 +1,62 @@
+"use strict";
+
+test(() => {
+  const target = new EventTarget();
+  const event = new Event("foo", { bubbles: true, cancelable: false });
+  let callCount = 0;
+
+  function listener(e) {
+    assert_equals(e, event);
+    ++callCount;
+  }
+
+  target.addEventListener("foo", listener);
+
+  target.dispatchEvent(event);
+  assert_equals(callCount, 1);
+
+  target.dispatchEvent(event);
+  assert_equals(callCount, 2);
+
+  target.removeEventListener("foo", listener);
+  target.dispatchEvent(event);
+  assert_equals(callCount, 2);
+}, "A constructed EventTarget can be used as expected");
+
+test(() => {
+  class NicerEventTarget extends EventTarget {
+    on(...args) {
+      this.addEventListener(...args);
+    }
+
+    off(...args) {
+      this.removeEventListener(...args);
+    }
+
+    dispatch(type, detail) {
+      this.dispatchEvent(new CustomEvent(type, { detail }));
+    }
+  }
+
+  const target = new NicerEventTarget();
+  const event = new Event("foo", { bubbles: true, cancelable: false });
+  const detail = "some data";
+  let callCount = 0;
+
+  function listener(e) {
+    assert_equals(e.detail, detail);
+    ++callCount;
+  }
+
+  target.on("foo", listener);
+
+  target.dispatch("foo", detail);
+  assert_equals(callCount, 1);
+
+  target.dispatch("foo", detail);
+  assert_equals(callCount, 2);
+
+  target.off("foo", listener);
+  target.dispatch("foo", detail);
+  assert_equals(callCount, 2);
+}, "EventTarget can be subclassed");
diff --git a/testing/web-platform/tests/dom/events/EventTarget-dispatchEvent-returnvalue.html b/testing/web-platform/tests/dom/events/EventTarget-dispatchEvent-returnvalue.html
new file mode 100644
index 0000000000..c4466e0d6c
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventTarget-dispatchEvent-returnvalue.html
@@ -0,0 +1,71 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>EventTarget.dispatchEvent: return value</title>
+<link rel="help" href="https://dom.spec.whatwg.org/#concept-event-dispatch">
+<link rel="help" href="https://dom.spec.whatwg.org/#dom-event-preventdefault">
+<link rel="help" href="https://dom.spec.whatwg.org/#dom-event-returnvalue">
+<link rel="help" href="https://dom.spec.whatwg.org/#dom-event-defaultprevented">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id=log></div>
+<table id="table" border="1" style="display: none">
+    <tbody id="table-body">
+    <tr id="table-row">
+        <td id="table-cell">Shady Grove</td>
+        <td>Aeolian</td>
+    </tr>
+    <tr id="parent">
+        <td id="target">Over the river, Charlie</td>
+        <td>Dorian</td>
+    </tr>
+    </tbody>
+</table>
+<script>
+test(function() {
+    var event_type = "foo";
+    var target = document.getElementById("target");
+    var parent = document.getElementById("parent");
+    var default_prevented;
+    var return_value;
+
+    parent.addEventListener(event_type, function(e) {}, true);
+    target.addEventListener(event_type, function(e) {
+        evt.preventDefault();
+        default_prevented = evt.defaultPrevented;
+        return_value = evt.returnValue;
+    }, true);
+    target.addEventListener(event_type, function(e) {}, true);
+
+    var evt = document.createEvent("Event");
+    evt.initEvent(event_type, true, true);
+
+    assert_true(parent.dispatchEvent(evt));
+    assert_false(target.dispatchEvent(evt));
+    assert_true(default_prevented);
+    assert_false(return_value);
+}, "Return value of EventTarget.dispatchEvent() affected by preventDefault().");
+
+test(function() {
+    var event_type = "foo";
+    var target = document.getElementById("target");
+    var parent = document.getElementById("parent");
+    var default_prevented;
+    var return_value;
+
+    parent.addEventListener(event_type, function(e) {}, true);
+    target.addEventListener(event_type, function(e) {
+        evt.returnValue = false;
+        default_prevented = evt.defaultPrevented;
+        return_value = evt.returnValue;
+    }, true);
+    target.addEventListener(event_type, function(e) {}, true);
+
+    var evt = document.createEvent("Event");
+    evt.initEvent(event_type, true, true);
+
+    assert_true(parent.dispatchEvent(evt));
+    assert_false(target.dispatchEvent(evt));
+    assert_true(default_prevented);
+    assert_false(return_value);
+}, "Return value of EventTarget.dispatchEvent() affected by returnValue.");
+</script>
diff --git a/testing/web-platform/tests/dom/events/EventTarget-dispatchEvent.html b/testing/web-platform/tests/dom/events/EventTarget-dispatchEvent.html
new file mode 100644
index 0000000000..783561f5fb
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventTarget-dispatchEvent.html
@@ -0,0 +1,104 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>EventTarget.dispatchEvent</title>
+<link rel="author" title="Olli Pettay" href="mailto:Olli.Pettay@gmail.com">
+<link rel="author" title="Ms2ger" href="mailto:Ms2ger@gmail.com">
+<link rel="help" href="https://dom.spec.whatwg.org/#dom-eventtarget-dispatchevent">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/dom/nodes/Document-createEvent.js"></script>
+<div id="log"></div>
+<script>
+setup({
+  "allow_uncaught_exception": true,
+})
+
+test(function() {
+  assert_throws_js(TypeError, function() { document.dispatchEvent(null) })
+}, "Calling dispatchEvent(null).")
+
+for (var alias in aliases) {
+  test(function() {
+    var e = document.createEvent(alias)
+    assert_equals(e.type, "", "Event type should be empty string before initialization")
+    assert_throws_dom("InvalidStateError", function() { document.dispatchEvent(e) })
+  }, "If the event's initialized flag is not set, an InvalidStateError must be thrown (" + alias + ").")
+}
+
+var dispatch_dispatch = async_test("If the event's dispatch flag is set, an InvalidStateError must be thrown.")
+dispatch_dispatch.step(function() {
+  var e = document.createEvent("Event")
+  e.initEvent("type", false, false)
+
+  var target = document.createElement("div")
+  target.addEventListener("type", dispatch_dispatch.step_func(function() {
+    assert_throws_dom("InvalidStateError", function() {
+      target.dispatchEvent(e)
+    })
+    assert_throws_dom("InvalidStateError", function() {
+      document.dispatchEvent(e)
+    })
+  }), false)
+
+  assert_equals(target.dispatchEvent(e), true, "dispatchEvent must return true")
+
+  dispatch_dispatch.done()
+})
+
+test(function() {
+  // https://www.w3.org/Bugs/Public/show_bug.cgi?id=17713
+  // https://www.w3.org/Bugs/Public/show_bug.cgi?id=17714
+
+  var e = document.createEvent("Event")
+  e.initEvent("type", false, false)
+
+  var called = []
+
+  var target = document.createElement("div")
+  target.addEventListener("type", function() {
+    called.push("First")
+    throw new Error()
+  }, false)
+
+  target.addEventListener("type", function() {
+    called.push("Second")
+  }, false)
+
+  assert_equals(target.dispatchEvent(e), true, "dispatchEvent must return true")
+  assert_array_equals(called, ["First", "Second"],
+                      "Should have continued to call other event listeners")
+}, "Exceptions from event listeners must not be propagated.")
+
+async_test(function() {
+  var results = []
+  var outerb = document.createElement("b")
+  var middleb = outerb.appendChild(document.createElement("b"))
+  var innerb = middleb.appendChild(document.createElement("b"))
+  outerb.addEventListener("x", this.step_func(function() {
+    middleb.addEventListener("x", this.step_func(function() {
+      results.push("middle")
+    }), true)
+    results.push("outer")
+  }), true)
+  innerb.dispatchEvent(new Event("x"))
+  assert_array_equals(results, ["outer", "middle"])
+  this.done()
+}, "Event listeners added during dispatch should be called");
+
+async_test(function() {
+  var results = []
+  var b = document.createElement("b")
+  b.addEventListener("x", this.step_func(function() {
+    results.push(1)
+  }), true)
+  b.addEventListener("x", this.step_func(function() {
+    results.push(2)
+  }), false)
+  b.addEventListener("x", this.step_func(function() {
+    results.push(3)
+  }), true)
+  b.dispatchEvent(new Event("x"))
+  assert_array_equals(results, [1, 3, 2])
+  this.done()
+}, "Capturing event listeners should be called before non-capturing ones")
+</script>
diff --git a/testing/web-platform/tests/dom/events/EventTarget-removeEventListener.any.js b/testing/web-platform/tests/dom/events/EventTarget-removeEventListener.any.js
new file mode 100644
index 0000000000..289dfcfbab
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventTarget-removeEventListener.any.js
@@ -0,0 +1,8 @@
+// META: title=EventTarget.removeEventListener
+
+// Step 1.
+test(function() {
+  assert_equals(globalThis.removeEventListener("x", null, false), undefined);
+  assert_equals(globalThis.removeEventListener("x", null, true), undefined);
+  assert_equals(globalThis.removeEventListener("x", null), undefined);
+}, "removing a null event listener should succeed");
diff --git a/testing/web-platform/tests/dom/events/EventTarget-this-of-listener.html b/testing/web-platform/tests/dom/events/EventTarget-this-of-listener.html
new file mode 100644
index 0000000000..506564c413
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/EventTarget-this-of-listener.html
@@ -0,0 +1,182 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>EventTarget listeners this value</title>
+<link rel="author" title="Domenic Denicola" href="mailto:d@domenic.me">
+<link rel="help" href="https://dom.spec.whatwg.org/#concept-event-listener-invoke">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<script>
+"use strict";
+
+test(() => {
+
+  const nodes = [
+    document.createElement("p"),
+    document.createTextNode("some text"),
+    document.createDocumentFragment(),
+    document.createComment("a comment"),
+    document.createProcessingInstruction("target", "data")
+  ];
+
+  let callCount = 0;
+  for (const node of nodes) {
+    node.addEventListener("someevent", function () {
+      ++callCount;
+      assert_equals(this, node);
+    });
+
+    node.dispatchEvent(new CustomEvent("someevent"));
+  }
+
+  assert_equals(callCount, nodes.length);
+
+}, "the this value inside the event listener callback should be the node");
+
+test(() => {
+
+  const nodes = [
+    document.createElement("p"),
+    document.createTextNode("some text"),
+    document.createDocumentFragment(),
+    document.createComment("a comment"),
+    document.createProcessingInstruction("target", "data")
+  ];
+
+  let callCount = 0;
+  for (const node of nodes) {
+    const handler = {
+      handleEvent() {
+        ++callCount;
+        assert_equals(this, handler);
+      }
+    };
+
+    node.addEventListener("someevent", handler);
+
+    node.dispatchEvent(new CustomEvent("someevent"));
+  }
+
+  assert_equals(callCount, nodes.length);
+
+}, "the this value inside the event listener object handleEvent should be the object");
+
+test(() => {
+
+  const nodes = [
+    document.createElement("p"),
+    document.createTextNode("some text"),
+    document.createDocumentFragment(),
+    document.createComment("a comment"),
+    document.createProcessingInstruction("target", "data")
+  ];
+
+  let callCount = 0;
+  for (const node of nodes) {
+    const handler = {
+      handleEvent() {
+        assert_unreached("should not call the old handleEvent method");
+      }
+    };
+
+    node.addEventListener("someevent", handler);
+    handler.handleEvent = function () {
+      ++callCount;
+      assert_equals(this, handler);
+    };
+
+    node.dispatchEvent(new CustomEvent("someevent"));
+  }
+
+  assert_equals(callCount, nodes.length);
+
+}, "dispatchEvent should invoke the current handleEvent method of the object");
+
+test(() => {
+
+  const nodes = [
+    document.createElement("p"),
+    document.createTextNode("some text"),
+    document.createDocumentFragment(),
+    document.createComment("a comment"),
+    document.createProcessingInstruction("target", "data")
+  ];
+
+  let callCount = 0;
+  for (const node of nodes) {
+    const handler = {};
+
+    node.addEventListener("someevent", handler);
+    handler.handleEvent = function () {
+      ++callCount;
+      assert_equals(this, handler);
+    };
+
+    node.dispatchEvent(new CustomEvent("someevent"));
+  }
+
+  assert_equals(callCount, nodes.length);
+
+}, "addEventListener should not require handleEvent to be defined on object listeners");
+
+test(() => {
+
+  const nodes = [
+    document.createElement("p"),
+    document.createTextNode("some text"),
+    document.createDocumentFragment(),
+    document.createComment("a comment"),
+    document.createProcessingInstruction("target", "data")
+  ];
+
+  let callCount = 0;
+  for (const node of nodes) {
+    function handler() {
+      ++callCount;
+      assert_equals(this, node);
+    }
+
+    handler.handleEvent = () => {
+      assert_unreached("should not call the handleEvent method on a function");
+    };
+
+    node.addEventListener("someevent", handler);
+
+    node.dispatchEvent(new CustomEvent("someevent"));
+  }
+
+  assert_equals(callCount, nodes.length);
+
+}, "handleEvent properties added to a function before addEventListener are not reached");
+
+test(() => {
+
+  const nodes = [
+    document.createElement("p"),
+    document.createTextNode("some text"),
+    document.createDocumentFragment(),
+    document.createComment("a comment"),
+    document.createProcessingInstruction("target", "data")
+  ];
+
+  let callCount = 0;
+  for (const node of nodes) {
+    function handler() {
+      ++callCount;
+      assert_equals(this, node);
+    }
+
+    node.addEventListener("someevent", handler);
+
+    handler.handleEvent = () => {
+      assert_unreached("should not call the handleEvent method on a function");
+    };
+
+    node.dispatchEvent(new CustomEvent("someevent"));
+  }
+
+  assert_equals(callCount, nodes.length);
+
+}, "handleEvent properties added to a function after addEventListener are not reached");
+
+</script>
diff --git a/testing/web-platform/tests/dom/events/KeyEvent-initKeyEvent.html b/testing/web-platform/tests/dom/events/KeyEvent-initKeyEvent.html
new file mode 100644
index 0000000000..3fffaba014
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/KeyEvent-initKeyEvent.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>KeyEvent.initKeyEvent</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+// The legacy KeyEvent.initKeyEvent shouldn't be defined in the wild anymore.
+// https://www.w3.org/TR/1999/WD-DOM-Level-2-19990923/events.html#Events-Event-initKeyEvent
+test(function() {
+  const event = document.createEvent("KeyboardEvent");
+  assert_true(event?.initKeyEvent === undefined);
+}, "KeyboardEvent.initKeyEvent shouldn't be defined (created by createEvent(\"KeyboardEvent\")");
+
+test(function() {
+  const event = new KeyboardEvent("keypress");
+  assert_true(event?.initKeyEvent === undefined);
+}, "KeyboardEvent.initKeyEvent shouldn't be defined (created by constructor)");
+
+test(function() {
+  assert_true(KeyboardEvent.prototype.initKeyEvent === undefined);
+}, "KeyboardEvent.prototype.initKeyEvent shouldn't be defined");
+</script>
diff --git a/testing/web-platform/tests/dom/events/event-disabled-dynamic.html b/testing/web-platform/tests/dom/events/event-disabled-dynamic.html
new file mode 100644
index 0000000000..3f995b02f1
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/event-disabled-dynamic.html
@@ -0,0 +1,21 @@
+<!doctype html>
+<meta charset=utf-8>
+<title>Test that disabled is honored immediately in presence of dynamic changes</title>
+<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
+<link rel="author" title="Andreas Farre" href="mailto:afarre@mozilla.com">
+<link rel="help" href="https://html.spec.whatwg.org/multipage/#enabling-and-disabling-form-controls:-the-disabled-attribute">
+<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1405087">
+<script src=/resources/testharness.js></script>
+<script src=/resources/testharnessreport.js></script>
+<input type="button" value="Click" disabled>
+<script>
+async_test(t => {
+  // NOTE: This test will timeout if it fails.
+  window.addEventListener('load', t.step_func(() => {
+    let e = document.querySelector('input');
+    e.disabled = false;
+    e.onclick = t.step_func_done(() => {});
+    e.click();
+  }));
+}, "disabled is honored properly in presence of dynamic changes");
+</script>
diff --git a/testing/web-platform/tests/dom/events/event-global-extra.window.js b/testing/web-platform/tests/dom/events/event-global-extra.window.js
new file mode 100644
index 0000000000..0f14961c40
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/event-global-extra.window.js
@@ -0,0 +1,90 @@
+const otherWindow = document.body.appendChild(document.createElement("iframe")).contentWindow;
+
+["EventTarget", "XMLHttpRequest"].forEach(constructorName => {
+  async_test(t => {
+    const eventTarget = new otherWindow[constructorName]();
+    eventTarget.addEventListener("hi", t.step_func_done(e => {
+      assert_equals(otherWindow.event, undefined);
+      assert_equals(e, window.event);
+    }));
+    eventTarget.dispatchEvent(new Event("hi"));
+  }, "window.event for constructors from another global: " + constructorName);
+});
+
+// XXX: It would be good to test a subclass of EventTarget once we sort out
+// https://github.com/heycam/webidl/issues/540
+
+async_test(t => {
+  const element = document.body.appendChild(otherWindow.document.createElement("meh"));
+  element.addEventListener("yo", t.step_func_done(e => {
+    assert_equals(e, window.event);
+  }));
+  element.dispatchEvent(new Event("yo"));
+}, "window.event and element from another document");
+
+async_test(t => {
+  const doc = otherWindow.document,
+        element = doc.body.appendChild(doc.createElement("meh")),
+        child = element.appendChild(doc.createElement("bleh"));
+  element.addEventListener("yoyo", t.step_func(e => {
+    document.body.appendChild(element);
+    assert_equals(element.ownerDocument, document);
+    assert_equals(window.event, e);
+    assert_equals(otherWindow.event, undefined);
+  }), true);
+  element.addEventListener("yoyo", t.step_func(e => {
+    assert_equals(element.ownerDocument, document);
+    assert_equals(window.event, e);
+    assert_equals(otherWindow.event, undefined);
+  }), true);
+  child.addEventListener("yoyo", t.step_func_done(e => {
+    assert_equals(child.ownerDocument, document);
+    assert_equals(window.event, e);
+    assert_equals(otherWindow.event, undefined);
+  }));
+  child.dispatchEvent(new Event("yoyo"));
+}, "window.event and moving an element post-dispatch");
+
+test(t => {
+  const host = document.createElement("div"),
+        shadow = host.attachShadow({ mode: "open" }),
+        child = shadow.appendChild(document.createElement("trala")),
+        furtherChild = child.appendChild(document.createElement("waddup"));
+  let counter = 0;
+  host.addEventListener("hi", t.step_func(e => {
+    assert_equals(window.event, e);
+    assert_equals(counter++, 3);
+  }));
+  child.addEventListener("hi", t.step_func(e => {
+    assert_equals(window.event, undefined);
+    assert_equals(counter++, 2);
+  }));
+  furtherChild.addEventListener("hi", t.step_func(e => {
+    host.appendChild(child);
+    assert_equals(window.event, undefined);
+    assert_equals(counter++, 0);
+  }));
+  furtherChild.addEventListener("hi", t.step_func(e => {
+    assert_equals(window.event, undefined);
+    assert_equals(counter++, 1);
+  }));
+  furtherChild.dispatchEvent(new Event("hi", { composed: true, bubbles: true }));
+  assert_equals(counter, 4);
+}, "window.event should not be affected by nodes moving post-dispatch");
+
+async_test(t => {
+  const frame = document.body.appendChild(document.createElement("iframe"));
+  frame.src = "resources/event-global-extra-frame.html";
+  frame.onload = t.step_func_done((load_event) => {
+    const event = new Event("hi");
+    document.addEventListener("hi", frame.contentWindow.listener); // listener intentionally not wrapped in t.step_func
+    document.addEventListener("hi", t.step_func(e => {
+      assert_equals(event, e);
+      assert_equals(window.event, e);
+    }));
+    document.dispatchEvent(event);
+    assert_equals(frameState.event, event);
+    assert_equals(frameState.windowEvent, event);
+    assert_equals(frameState.parentEvent, load_event);
+  });
+}, "Listener from a different global");
diff --git a/testing/web-platform/tests/dom/events/event-global-is-still-set-when-coercing-beforeunload-result.html b/testing/web-platform/tests/dom/events/event-global-is-still-set-when-coercing-beforeunload-result.html
new file mode 100644
index 0000000000..a64c8b6b8b
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/event-global-is-still-set-when-coercing-beforeunload-result.html
@@ -0,0 +1,23 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>window.event is still set when 'beforeunload' result is coerced to string</title>
+<link rel="help" href="https://dom.spec.whatwg.org/#ref-for-window-current-event%E2%91%A1">
+<link rel="help" href="https://webidl.spec.whatwg.org/#call-a-user-objects-operation">
+
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<iframe id="iframe" src="resources/event-global-is-still-set-when-coercing-beforeunload-result-frame.html"></iframe>
+<body>
+<script>
+window.onload = () => {
+  async_test(t => {
+    iframe.onload = t.step_func_done(() => {
+      assert_equals(typeof window.currentEventInToString, "object");
+      assert_equals(window.currentEventInToString.type, "beforeunload");
+    });
+
+    iframe.contentWindow.location.href = "about:blank";
+  });
+};
+</script>
diff --git a/testing/web-platform/tests/dom/events/event-global-is-still-set-when-reporting-exception-onerror.html b/testing/web-platform/tests/dom/events/event-global-is-still-set-when-reporting-exception-onerror.html
new file mode 100644
index 0000000000..ceaac4fe2b
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/event-global-is-still-set-when-reporting-exception-onerror.html
@@ -0,0 +1,43 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>window.onerror handler restores window.event after it reports an exception</title>
+<link rel="help" href="https://dom.spec.whatwg.org/#concept-event-listener-inner-invoke">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body>
+<iframe src="resources/empty-document.html"></iframe>
+<iframe src="resources/empty-document.html"></iframe>
+
+<script>
+setup({ allow_uncaught_exception: true });
+
+async_test(t => {
+    window.onload = t.step_func_done(onLoadEvent => {
+        frames[0].onerror = new frames[1].Function(`
+            top.eventDuringSecondOnError = top.window.event;
+            top.frames[0].eventDuringSecondOnError = top.frames[0].event;
+            top.frames[1].eventDuringSecondOnError = top.frames[1].event;
+        `);
+
+        window.onerror = new frames[0].Function(`
+            top.eventDuringFirstOnError = top.window.event;
+            top.frames[0].eventDuringFirstOnError = top.frames[0].event;
+            top.frames[1].eventDuringFirstOnError = top.frames[1].event;
+
+            foo; // cause second onerror
+        `);
+
+        const myEvent = new ErrorEvent("error", { error: new Error("myError") });
+        window.dispatchEvent(myEvent);
+
+        assert_equals(top.eventDuringFirstOnError, onLoadEvent);
+        assert_equals(frames[0].eventDuringFirstOnError, myEvent);
+        assert_equals(frames[1].eventDuringFirstOnError, undefined);
+
+        assert_equals(top.eventDuringSecondOnError, onLoadEvent);
+        assert_equals(frames[0].eventDuringSecondOnError, myEvent);
+        assert_equals(frames[1].eventDuringSecondOnError.error.name, "ReferenceError");
+    });
+});
+</script>
diff --git a/testing/web-platform/tests/dom/events/event-global-set-before-handleEvent-lookup.window.js b/testing/web-platform/tests/dom/events/event-global-set-before-handleEvent-lookup.window.js
new file mode 100644
index 0000000000..8f934bcea9
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/event-global-set-before-handleEvent-lookup.window.js
@@ -0,0 +1,19 @@
+// https://dom.spec.whatwg.org/#concept-event-listener-inner-invoke (steps 8.2 - 12)
+// https://webidl.spec.whatwg.org/#call-a-user-objects-operation (step 10.1)
+
+test(() => {
+  const eventTarget = new EventTarget;
+
+  let currentEvent;
+  eventTarget.addEventListener("foo", {
+    get handleEvent() {
+      currentEvent = window.event;
+      return () => {};
+    }
+  });
+
+  const event = new Event("foo");
+  eventTarget.dispatchEvent(event);
+
+  assert_equals(currentEvent, event);
+}, "window.event is set before 'handleEvent' lookup");
diff --git a/testing/web-platform/tests/dom/events/event-global.html b/testing/web-platform/tests/dom/events/event-global.html
new file mode 100644
index 0000000000..3e8d25ecb5
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/event-global.html
@@ -0,0 +1,117 @@
+<!DOCTYPE html>
+<title>window.event tests</title>
+<link rel="author" title="Mike Taylor" href="mailto:miketaylr@gmail.com">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id=log></div>
+<script>
+setup({allow_uncaught_exception: true});
+
+test(t => {
+  assert_own_property(window, "event");
+  assert_equals(window.event, undefined);
+}, "event exists on window, which is initially set to undefined");
+
+async_test(t => {
+  let target = document.createElement("div");
+  assert_equals(window.event, undefined, "undefined before dispatch");
+
+  let clickEvent = new Event("click");
+  target.addEventListener("click", t.step_func_done(e => {
+    assert_equals(window.event, clickEvent, "window.event set to current event during dispatch");
+  }));
+
+  target.dispatchEvent(clickEvent);
+  assert_equals(window.event, undefined, "undefined after dispatch");
+}, "window.event is only defined during dispatch");
+
+async_test(t => {
+  let parent = document.createElement("div");
+  let root = parent.attachShadow({mode: "closed"});
+  let span = document.createElement("span");
+  root.appendChild(span);
+
+  span.addEventListener("test", t.step_func(e => {
+    assert_equals(window.event, undefined);
+    assert_not_equals(window.event, e);
+  }));
+
+  parent.addEventListener("test", t.step_func_done(e => {
+    assert_equals(window.event, e);
+    assert_not_equals(window.event, undefined);
+  }));
+
+  parent.dispatchEvent(new Event("test", {composed: true}));
+}, "window.event is undefined if the target is in a shadow tree (event dispatched outside shadow tree)");
+
+async_test(t => {
+  let parent = document.createElement("div");
+  let root = parent.attachShadow({mode: "closed"});
+  let span = document.createElement("span");
+  root.appendChild(span);
+  let shadowNode = root.firstElementChild;
+
+  shadowNode.addEventListener("test", t.step_func((e) => {
+    assert_not_equals(window.event, e);
+    assert_equals(window.event, undefined);
+  }));
+
+  parent.addEventListener("test", t.step_func_done(e => {
+    assert_equals(window.event, e);
+    assert_not_equals(window.event, undefined);
+  }));
+
+  shadowNode.dispatchEvent(new Event("test", {composed: true, bubbles: true}));
+}, "window.event is undefined if the target is in a shadow tree (event dispatched inside shadow tree)");
+
+async_test(t => {
+  let parent = document.createElement("div");
+  let root = parent.attachShadow({mode: "open"});
+  document.body.append(parent)
+  let span = document.createElement("span");
+  root.append(span);
+  let shadowNode = root.firstElementChild;
+
+  shadowNode.addEventListener("error", t.step_func(e => {
+    assert_not_equals(window.event, e);
+    assert_equals(window.event, undefined);
+  }));
+
+  let windowOnErrorCalled = false;
+  window.onerror = t.step_func_done(() => {
+    windowOnErrorCalled = true;
+    assert_equals(typeof window.event, "object");
+    assert_equals(window.event.type, "error");
+  });
+
+  shadowNode.dispatchEvent(new ErrorEvent("error", {composed: true, bubbles: true}));
+  assert_true(windowOnErrorCalled);
+}, "window.event is undefined inside window.onerror if the target is in a shadow tree (ErrorEvent dispatched inside shadow tree)");
+
+async_test(t => {
+  let target1 = document.createElement("div");
+  let target2 = document.createElement("div");
+
+  target2.addEventListener("dude", t.step_func(() => {
+    assert_equals(window.event.type, "dude");
+  }));
+
+  target1.addEventListener("cool", t.step_func_done(() => {
+    assert_equals(window.event.type, "cool", "got expected event from global event during dispatch");
+    target2.dispatchEvent(new Event("dude"));
+    assert_equals(window.event.type, "cool", "got expected event from global event after handling a different event handler callback");
+  }));
+
+  target1.dispatchEvent(new Event("cool"));
+}, "window.event is set to the current event during dispatch");
+
+async_test(t => {
+  let target = document.createElement("div");
+
+  target.addEventListener("click", t.step_func_done(e => {
+    assert_equals(e, window.event);
+  }));
+
+  target.dispatchEvent(new Event("click"));
+}, "window.event is set to the current event, which is the event passed to dispatch");
+</script>
diff --git a/testing/web-platform/tests/dom/events/event-global.worker.js b/testing/web-platform/tests/dom/events/event-global.worker.js
new file mode 100644
index 0000000000..116cf32932
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/event-global.worker.js
@@ -0,0 +1,14 @@
+importScripts("/resources/testharness.js");
+test(t => {
+  let seen = false;
+  const event = new Event("hi");
+  assert_equals(self.event, undefined);
+  self.addEventListener("hi", t.step_func(e => {
+    seen = true;
+    assert_equals(self.event, undefined);
+    assert_equals(e, event);
+  }));
+  self.dispatchEvent(event);
+  assert_true(seen);
+}, "There's no self.event (that's why we call it window.event) in workers");
+done();
diff --git a/testing/web-platform/tests/dom/events/focus-event-document-move.html b/testing/web-platform/tests/dom/events/focus-event-document-move.html
new file mode 100644
index 0000000000..2943761ce1
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/focus-event-document-move.html
@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<link rel="author" href="mailto:masonf@chromium.org">
+<link rel="help" href="https://crbug.com/747207">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+
+<script>
+  function handleDown(node) {
+    var d2 = new Document();
+    d2.appendChild(node);
+  }
+</script>
+
+<!-- No crash should occur if a node is moved during mousedown. -->
+<div id='click' onmousedown='handleDown(this)'>Click me</div>
+
+<script>
+  const target = document.getElementById('click');
+  async_test(t => {
+    let actions = new test_driver.Actions()
+      .pointerMove(0, 0, {origin: target})
+      .pointerDown()
+      .pointerUp()
+      .send()
+      .then(t.step_func_done(() => {
+        assert_equals(null,document.getElementById('click'));
+      }))
+      .catch(e => t.step_func(() => assert_unreached('Error')));
+  },'Moving a node during mousedown should not crash');
+</script>
diff --git a/testing/web-platform/tests/dom/events/keypress-dispatch-crash.html b/testing/web-platform/tests/dom/events/keypress-dispatch-crash.html
new file mode 100644
index 0000000000..3207adbd8c
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/keypress-dispatch-crash.html
@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+<link rel="author" title="Robert Flack" href="mailto:flackr@chromium.org">
+<link rel="help" href="https://bugs.chromium.org/p/chromium/issues/detail?id=1209098">
+
+<!-- No crash should occur if a keypress is dispatched to a constructed document. -->
+
+<script>
+var newDoc = document.implementation.createDocument( "", null);
+var testNode = newDoc.createElement('div');
+newDoc.append(testNode);
+
+var syntheticEvent = document.createEvent('KeyboardEvents');
+syntheticEvent.initKeyboardEvent("keypress");
+testNode.dispatchEvent(syntheticEvent)
+</script>
diff --git a/testing/web-platform/tests/dom/events/legacy-pre-activation-behavior.window.js b/testing/web-platform/tests/dom/events/legacy-pre-activation-behavior.window.js
new file mode 100644
index 0000000000..e9e84bfad1
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/legacy-pre-activation-behavior.window.js
@@ -0,0 +1,10 @@
+test(t => {
+  const input = document.body.appendChild(document.createElement('input'));
+  input.type = "radio";
+  t.add_cleanup(() => input.remove());
+  const clickEvent = new MouseEvent('click', { button: 0, which: 1 });
+  input.addEventListener('change', t.step_func(() => {
+    assert_equals(clickEvent.eventPhase, Event.NONE);
+  }));
+  input.dispatchEvent(clickEvent);
+}, "Use NONE phase during legacy-pre-activation behavior");
diff --git a/testing/web-platform/tests/dom/events/mouse-event-retarget.html b/testing/web-platform/tests/dom/events/mouse-event-retarget.html
new file mode 100644
index 0000000000..c9ce6240d4
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/mouse-event-retarget.html
@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<html>
+<title>Script created MouseEvent properly retargets and adjusts offsetX</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<style>
+body {
+  margin: 8px;
+  padding: 0;
+}
+</style>
+
+<div id="target">Hello</div>
+
+<script>
+async_test(t => {
+  target.addEventListener('click', ev => {
+    t.step(() => assert_equals(ev.offsetX, 42));
+    t.done();
+  });
+
+  const ev = new MouseEvent('click', { clientX: 50 });
+  target.dispatchEvent(ev);
+}, "offsetX is correctly adjusted");
+</script>
diff --git a/testing/web-platform/tests/dom/events/no-focus-events-at-clicking-editable-content-in-link.html b/testing/web-platform/tests/dom/events/no-focus-events-at-clicking-editable-content-in-link.html
new file mode 100644
index 0000000000..dc08636c46
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/no-focus-events-at-clicking-editable-content-in-link.html
@@ -0,0 +1,80 @@
+<!doctype html>
+<html>
+<head>
+<meta chareset="utf-8">
+<title>Clicking editable content in link shouldn't cause redundant focus related events</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+</head>
+<body>
+<a href="#"><span contenteditable>Hello</span></a>
+<a href="#" contenteditable><span>Hello</span></a>
+<script>
+function promiseTicks() {
+  return new Promise(resolve => {
+    requestAnimationFrame(() => {
+      requestAnimationFrame(resolve);
+    });
+  });
+}
+
+async function clickElementAndCollectFocusEvents(x, y, options) {
+  await promiseTicks();
+  let events = [];
+  for (const eventType of ["focus", "blur", "focusin", "focusout"]) {
+    document.addEventListener(eventType, event => {
+      events.push(`type: ${event.type}, target: ${event.target.nodeName}`);
+    }, {capture: true});
+  }
+
+  const waitForClickEvent = new Promise(resolve => {
+    addEventListener("click", resolve, {capture: true, once: true});
+  });
+
+  await new test_driver
+    .Actions()
+    .pointerMove(x, y, options)
+    .pointerDown()
+    .pointerUp()
+    .send();
+
+  await waitForClickEvent;
+  await promiseTicks();
+  return events;
+}
+
+promise_test(async t => {
+  document.activeElement?.blur();
+  const editingHost = document.querySelector("span[contenteditable]");
+  editingHost.blur();
+  const focusEvents =
+    await clickElementAndCollectFocusEvents(5, 5, {origin: editingHost});
+  assert_array_equals(
+    focusEvents,
+    [
+      "type: focus, target: SPAN",
+      "type: focusin, target: SPAN",
+    ],
+    "Click event shouldn't cause redundant focus events");
+}, "Click editable element in link");
+
+promise_test(async t => {
+  document.activeElement?.blur();
+  const editingHost = document.querySelector("a[contenteditable]");
+  editingHost.blur();
+  const focusEvents =
+    await clickElementAndCollectFocusEvents(5, 5, {origin: editingHost});
+  assert_array_equals(
+    focusEvents,
+    [
+      "type: focus, target: A",
+      "type: focusin, target: A",
+    ],
+    "Click event shouldn't cause redundant focus events");
+}, "Click editable link");
+</script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-body.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-body.html
new file mode 100644
index 0000000000..5574fe0acb
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-body.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<title>non-passive mousewheel event listener on body</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<link rel="help" href="https://github.com/w3c/uievents/issues/331">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.body,
+    eventName: 'mousewheel',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-div.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-div.html
new file mode 100644
index 0000000000..6fbf692cd7
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-div.html
@@ -0,0 +1,35 @@
+<!DOCTYPE html>
+<title>non-passive mousewheel event listener on div</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<link rel="help" href="https://github.com/w3c/uievents/issues/331">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<style>
+  html, body {
+    overflow: hidden;
+    margin: 0;
+  }
+  #div {
+    position: fixed;
+    top: 0;
+    right: 0;
+    bottom: 0;
+    left: 0;
+    overflow: scroll;
+  }
+</style>
+<div class=remove-on-cleanup id=div>
+  <div style="height: 200vh"></div>
+</div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.getElementById('div'),
+    eventName: 'mousewheel',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-document.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-document.html
new file mode 100644
index 0000000000..7d07393c69
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-document.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<title>non-passive mousewheel event listener on document</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<link rel="help" href="https://github.com/w3c/uievents/issues/331">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document,
+    eventName: 'mousewheel',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-root.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-root.html
new file mode 100644
index 0000000000..e85fbacaba
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-root.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<title>non-passive mousewheel event listener on root</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<link rel="help" href="https://github.com/w3c/uievents/issues/331">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.documentElement,
+    eventName: 'mousewheel',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-window.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-window.html
new file mode 100644
index 0000000000..29b09f8561
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-mousewheel-event-listener-on-window.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<title>non-passive mousewheel event listener on window</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<link rel="help" href="https://github.com/w3c/uievents/issues/331">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: window,
+    eventName: 'mousewheel',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-body.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-body.html
new file mode 100644
index 0000000000..f417bdd0a6
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-body.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>non-passive touchmove event listener on body</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.body,
+    eventName: 'touchmove',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-div.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-div.html
new file mode 100644
index 0000000000..11c9345407
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-div.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>non-passive touchmove event listener on div</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.getElementById('touchDiv'),
+    eventName: 'touchmove',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-document.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-document.html
new file mode 100644
index 0000000000..8b95a8d492
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-document.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>non-passive touchmove event listener on document</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document,
+    eventName: 'touchmove',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-root.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-root.html
new file mode 100644
index 0000000000..c41ab72bd8
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-root.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>non-passive touchmove event listener on root</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.documentElement,
+    eventName: 'touchmove',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-window.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-window.html
new file mode 100644
index 0000000000..3d6675c566
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchmove-event-listener-on-window.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<link rel="help" href="https://github.com/WICG/interventions/issues/35">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: window,
+    eventName: 'touchstart',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-body.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-body.html
new file mode 100644
index 0000000000..f6e6ecb06d
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-body.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>non-passive touchstart event listener on body</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.body,
+    eventName: 'touchstart',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-div.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-div.html
new file mode 100644
index 0000000000..2e7c6e6b3b
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-div.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>non-passive touchstart event listener on div</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.getElementById('touchDiv'),
+    eventName: 'touchstart',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-document.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-document.html
new file mode 100644
index 0000000000..22fcbdc322
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-document.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>non-passive touchstart event listener on document</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document,
+    eventName: 'touchstart',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-root.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-root.html
new file mode 100644
index 0000000000..56c51349a0
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-root.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>non-passive touchstart event listener on root</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.documentElement,
+    eventName: 'touchstart',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-window.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-window.html
new file mode 100644
index 0000000000..4e9d424a9d
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-touchstart-event-listener-on-window.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>non-passive touchstart event listener on window</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: window,
+    eventName: 'touchstart',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-body.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-body.html
new file mode 100644
index 0000000000..070cadc291
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-body.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<title>non-passive wheel event listener on body</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.body,
+    eventName: 'wheel',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-div.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-div.html
new file mode 100644
index 0000000000..c49d18ac13
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-div.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<title>non-passive wheel event listener on div</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<style>
+  html, body {
+    overflow: hidden;
+    margin: 0;
+  }
+  #div {
+    position: fixed;
+    top: 0;
+    right: 0;
+    bottom: 0;
+    left: 0;
+    overflow: scroll;
+  }
+</style>
+<div class=remove-on-cleanup id=div>
+  <div style="height: 200vh"></div>
+</div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.getElementById('div'),
+    eventName: 'wheel',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-document.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-document.html
new file mode 100644
index 0000000000..31a55cad43
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-document.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<title>non-passive wheel event listener on document</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document,
+    eventName: 'wheel',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-root.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-root.html
new file mode 100644
index 0000000000..b7bacbfc7c
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-root.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<title>non-passive wheel event listener on root</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.documentElement,
+    eventName: 'wheel',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-window.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-window.html
new file mode 100644
index 0000000000..c236059df4
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/non-passive-wheel-event-listener-on-window.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<title>non-passive wheel event listener on window</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: window,
+    eventName: 'wheel',
+    passive: false,
+    expectCancelable: true,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-body.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-body.html
new file mode 100644
index 0000000000..9db12cfbdc
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-body.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<title>passive mousewheel event listener on body</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<link rel="help" href="https://github.com/w3c/uievents/issues/331">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.body,
+    eventName: 'mousewheel',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-div.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-div.html
new file mode 100644
index 0000000000..373670856b
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-div.html
@@ -0,0 +1,35 @@
+<!DOCTYPE html>
+<title>passive mousewheel event listener on div</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<link rel="help" href="https://github.com/w3c/uievents/issues/331">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<style>
+  html, body {
+    overflow: hidden;
+    margin: 0;
+  }
+  #div {
+    position: fixed;
+    top: 0;
+    right: 0;
+    bottom: 0;
+    left: 0;
+    overflow: scroll;
+  }
+</style>
+<div class=remove-on-cleanup id=div>
+  <div style="height: 200vh"></div>
+</div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.getElementById('div'),
+    eventName: 'mousewheel',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-document.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-document.html
new file mode 100644
index 0000000000..71262280b6
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-document.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<title>passive mousewheel event listener on document</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<link rel="help" href="https://github.com/w3c/uievents/issues/331">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document,
+    eventName: 'mousewheel',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-root.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-root.html
new file mode 100644
index 0000000000..fc641d172e
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-root.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<title>passive mousewheel event listener on root</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<link rel="help" href="https://github.com/w3c/uievents/issues/331">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.documentElement,
+    eventName: 'mousewheel',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-window.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-window.html
new file mode 100644
index 0000000000..f60955c7c4
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-mousewheel-event-listener-on-window.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<title>passive mousewheel event listener on window</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<link rel="help" href="https://github.com/w3c/uievents/issues/331">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: window,
+    eventName: 'mousewheel',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-body.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-body.html
new file mode 100644
index 0000000000..2349bad258
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-body.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>passive touchmove event listener on body</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.body,
+    eventName: 'touchmove',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-div.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-div.html
new file mode 100644
index 0000000000..a61b34851e
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-div.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>passive touchmove event listener on div</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.getElementById('touchDiv'),
+    eventName: 'touchmove',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-document.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-document.html
new file mode 100644
index 0000000000..b49971b5b0
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-document.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>passive touchmove event listener on document</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document,
+    eventName: 'touchmove',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-root.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-root.html
new file mode 100644
index 0000000000..b851704590
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-root.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>passive touchmove event listener on root</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.documentElement,
+    eventName: 'touchmove',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-window.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-window.html
new file mode 100644
index 0000000000..351d6ace84
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchmove-event-listener-on-window.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>passive touchmove event listener on window</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: window,
+    eventName: 'touchstart',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-body.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-body.html
new file mode 100644
index 0000000000..c3d2b577fd
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-body.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>passive touchstart event listener on body</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.body,
+    eventName: 'touchstart',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-div.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-div.html
new file mode 100644
index 0000000000..103e7f0d23
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-div.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>passive touchstart event listener on div</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.getElementById('touchDiv'),
+    eventName: 'touchstart',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-document.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-document.html
new file mode 100644
index 0000000000..2e4de2405f
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-document.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>passive touchstart event listener on document</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document,
+    eventName: 'touchstart',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-root.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-root.html
new file mode 100644
index 0000000000..0f52e9a16f
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-root.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>passive touchstart event listener on root</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.documentElement,
+    eventName: 'touchstart',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-window.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-window.html
new file mode 100644
index 0000000000..c47af8101f
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-touchstart-event-listener-on-window.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>passive touchstart event listener on window</title>
+<link rel="help" href="https://w3c.github.io/touch-events/#cancelability">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/wait-for.js"></script>
+<script src="resources/touching.js"></script>
+<style>
+#touchDiv {
+  width: 100px;
+  height: 100px;
+}
+</style>
+<div id="touchDiv"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: window,
+    eventName: 'touchstart',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-body.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-body.html
new file mode 100644
index 0000000000..fe0869b022
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-body.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<title>passive wheel event listener on body</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.body,
+    eventName: 'wheel',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-div.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-div.html
new file mode 100644
index 0000000000..e2ca6e795a
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-div.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<title>passive wheel event listener on div</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<style>
+  html, body {
+    overflow: hidden;
+    margin: 0;
+  }
+  #div {
+    position: fixed;
+    top: 0;
+    right: 0;
+    bottom: 0;
+    left: 0;
+    overflow: scroll;
+  }
+</style>
+<div class=remove-on-cleanup id=div>
+  <div style="height: 200vh"></div>
+</div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.getElementById('div'),
+    eventName: 'wheel',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-document.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-document.html
new file mode 100644
index 0000000000..61b716f7bb
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-document.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<title>passive wheel event listener on document</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document,
+    eventName: 'wheel',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-root.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-root.html
new file mode 100644
index 0000000000..6b383bc871
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-root.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<title>passive wheel event listener on root</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: document.documentElement,
+    eventName: 'wheel',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-window.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-window.html
new file mode 100644
index 0000000000..a1e901f552
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/passive-wheel-event-listener-on-window.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<title>passive wheel event listener on window</title>
+<link rel="help" href="https://w3c.github.io/uievents/#cancelability-of-wheel-events">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/scrolling.js"></script>
+<div class=remove-on-cleanup style="height: 200vh"></div>
+<script>
+  document.body.onload = () => runTest({
+    target: window,
+    eventName: 'wheel',
+    passive: true,
+    expectCancelable: false,
+  });
+</script>
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/resources/scrolling.js b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/resources/scrolling.js
new file mode 100644
index 0000000000..88e10f5efd
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/resources/scrolling.js
@@ -0,0 +1,34 @@
+function raf() {
+  return new Promise((resolve) => {
+    // rAF twice.
+    window.requestAnimationFrame(() => {
+      window.requestAnimationFrame(resolve);
+    });
+  });
+}
+
+async function runTest({target, eventName, passive, expectCancelable}) {
+  await raf();
+
+  let cancelable = null;
+  let arrived = false;
+  target.addEventListener(eventName, function (event) {
+    cancelable = event.cancelable;
+    arrived = true;
+  }, {passive:passive, once:true});
+
+  promise_test(async (t) => {
+    t.add_cleanup(() => {
+      document.querySelector('.remove-on-cleanup')?.remove();
+    });
+    const pos_x = Math.floor(window.innerWidth / 2);
+    const pos_y = Math.floor(window.innerHeight / 2);
+    const delta_x = 0;
+    const delta_y = 100;
+
+    await new test_driver.Actions()
+      .scroll(pos_x, pos_y, delta_x, delta_y).send();
+    await t.step_wait(() => arrived, `Didn't get event ${eventName} on ${target.localName}`);
+    assert_equals(cancelable, expectCancelable);
+  });
+}
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/resources/touching.js b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/resources/touching.js
new file mode 100644
index 0000000000..620d26804b
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/resources/touching.js
@@ -0,0 +1,34 @@
+function waitForCompositorCommit() {
+  return new Promise((resolve) => {
+    // rAF twice.
+    window.requestAnimationFrame(() => {
+      window.requestAnimationFrame(resolve);
+    });
+  });
+}
+
+function injectInput(touchDiv) {
+  return new test_driver.Actions()
+    .addPointer("touch_pointer", "touch")
+    .pointerMove(0, 0, {origin: touchDiv})
+    .pointerDown()
+    .pointerMove(30, 30)
+    .pointerUp()
+    .send();
+}
+
+function runTest({target, eventName, passive, expectCancelable}) {
+  let touchDiv = document.getElementById("touchDiv");
+  let cancelable = null;
+  let arrived = false;
+  target.addEventListener(eventName, function (event) {
+    cancelable = event.cancelable;
+    arrived = true;
+  }, {passive});
+  promise_test(async () => {
+    await waitForCompositorCommit();
+    await injectInput(touchDiv);
+    await waitFor(() => arrived);
+    assert_equals(cancelable, expectCancelable);
+  });
+}
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/resources/wait-for.js b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/resources/wait-for.js
new file mode 100644
index 0000000000..0bf3e55834
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/resources/wait-for.js
@@ -0,0 +1,15 @@
+function waitFor(condition, MAX_FRAME = 500) {
+  return new Promise((resolve, reject) => {
+    function tick(frames) {
+      // We requestAnimationFrame either for MAX_FRAME frames or until condition is
+      // met.
+      if (frames >= MAX_FRAME)
+        reject(new Error(`Condition did not become true after ${MAX_FRAME} frames`));
+      else if (condition())
+        resolve();
+      else
+        requestAnimationFrame(() => tick(frames + 1));
+    }
+    tick(0);
+  });
+}
diff --git a/testing/web-platform/tests/dom/events/non-cancelable-when-passive/synthetic-events-cancelable.html b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/synthetic-events-cancelable.html
new file mode 100644
index 0000000000..4287770b8d
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/non-cancelable-when-passive/synthetic-events-cancelable.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<title>Synthetic events are always cancelable by default</title>
+<link rel="help" href="https://dom.spec.whatwg.org/#dictdef-eventinit">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+const eventsMap = {
+  wheel: 'WheelEvent',
+  mousewheel: 'WheelEvent',
+  touchstart: 'TouchEvent',
+  touchmove: 'TouchEvent',
+  touchend: 'TouchEvent',
+  touchcancel: 'TouchEvent',
+}
+function isCancelable(eventName, interfaceName) {
+  test(() => {
+    assert_implements(interfaceName in self, `${interfaceName} should be supported`);
+    let defaultPrevented = null;
+    addEventListener(eventName, event => {
+      event.preventDefault();
+      defaultPrevented = event.defaultPrevented;
+    });
+    const event = new self[interfaceName](eventName);
+    assert_false(event.cancelable, 'cancelable');
+    const dispatchEventReturnValue = dispatchEvent(event);
+    assert_false(defaultPrevented, 'defaultPrevented');
+    assert_true(dispatchEventReturnValue, 'dispatchEvent() return value');
+  }, `Synthetic ${eventName} event with interface ${interfaceName} is not cancelable`);
+}
+for (const eventName in eventsMap) {
+  isCancelable(eventName, eventsMap[eventName]);
+  isCancelable(eventName, 'Event');
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/passive-by-default.html b/testing/web-platform/tests/dom/events/passive-by-default.html
new file mode 100644
index 0000000000..02029f4dac
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/passive-by-default.html
@@ -0,0 +1,50 @@
+<!DOCTYPE html>
+<title>Default passive event listeners on window, document, document element, body</title>
+<link rel="help" href="https://dom.spec.whatwg.org/#default-passive-value">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+  <div id="div"></div>
+<script>
+  function isListenerPassive(eventName, eventTarget, passive, expectPassive) {
+    test(() => {
+      let defaultPrevented = null;
+      let handler = event => {
+        event.preventDefault();
+        defaultPrevented = event.defaultPrevented;
+        eventTarget.removeEventListener(eventName, handler);
+      };
+      if (passive === 'omitted') {
+        eventTarget.addEventListener(eventName, handler);
+      } else {
+        eventTarget.addEventListener(eventName, handler, {passive});
+      }
+      let dispatchEventReturnValue = eventTarget.dispatchEvent(new Event(eventName, {cancelable: true}));
+      assert_equals(defaultPrevented, !expectPassive, 'defaultPrevented');
+      assert_equals(dispatchEventReturnValue, expectPassive, 'dispatchEvent() return value');
+    }, `${eventName} listener is ${expectPassive ? '' : 'non-'}passive ${passive === 'omitted' ? 'by default' : `with {passive:${passive}}`} for ${eventTarget.constructor.name}`);
+  }
+
+  const eventNames = {
+    touchstart: true,
+    touchmove: true,
+    wheel: true,
+    mousewheel: true,
+    touchend: false
+  };
+  const passiveEventTargets = [window, document, document.documentElement, document.body];
+  const div = document.getElementById('div');
+
+  for (const eventName in eventNames) {
+    for (const eventTarget of passiveEventTargets) {
+      isListenerPassive(eventName, eventTarget, 'omitted', eventNames[eventName]);
+      isListenerPassive(eventName, eventTarget, undefined, eventNames[eventName]);
+      isListenerPassive(eventName, eventTarget, false, false);
+      isListenerPassive(eventName, eventTarget, true, true);
+    }
+    isListenerPassive(eventName, div, 'omitted', false);
+    isListenerPassive(eventName, div, undefined, false);
+    isListenerPassive(eventName, div, false, false);
+    isListenerPassive(eventName, div, true, true);
+  }
+</script>
diff --git a/testing/web-platform/tests/dom/events/relatedTarget.window.js b/testing/web-platform/tests/dom/events/relatedTarget.window.js
new file mode 100644
index 0000000000..ebc83ceb20
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/relatedTarget.window.js
@@ -0,0 +1,81 @@
+// https://dom.spec.whatwg.org/#concept-event-dispatch
+
+const host = document.createElement("div"),
+      child = host.appendChild(document.createElement("p")),
+      shadow = host.attachShadow({ mode: "closed" }),
+      slot = shadow.appendChild(document.createElement("slot"));
+
+test(() => {
+  for (target of [shadow, slot]) {
+    for (relatedTarget of [new XMLHttpRequest(), self, host]) {
+      const event = new FocusEvent("demo", { relatedTarget: relatedTarget });
+      target.dispatchEvent(event);
+      assert_equals(event.target, null);
+      assert_equals(event.relatedTarget, null);
+    }
+  }
+}, "Reset if target pointed to a shadow tree");
+
+test(() => {
+  for (relatedTarget of [shadow, slot]) {
+    for (target of [new XMLHttpRequest(), self, host]) {
+      const event = new FocusEvent("demo", { relatedTarget: relatedTarget });
+      target.dispatchEvent(event);
+      assert_equals(event.target, target);
+      assert_equals(event.relatedTarget, host);
+    }
+  }
+}, "Retarget a shadow-tree relatedTarget");
+
+test(t => {
+  const shadowChild = shadow.appendChild(document.createElement("div"));
+  shadowChild.addEventListener("demo", t.step_func(() => document.body.appendChild(shadowChild)));
+  const event = new FocusEvent("demo", { relatedTarget: new XMLHttpRequest() });
+  shadowChild.dispatchEvent(event);
+  assert_equals(shadowChild.parentNode, document.body);
+  assert_equals(event.target, null);
+  assert_equals(event.relatedTarget, null);
+  shadowChild.remove();
+}, "Reset if target pointed to a shadow tree pre-dispatch");
+
+test(t => {
+  const shadowChild = shadow.appendChild(document.createElement("div"));
+  document.body.addEventListener("demo", t.step_func(() => document.body.appendChild(shadowChild)));
+  const event = new FocusEvent("demo", { relatedTarget: shadowChild });
+  document.body.dispatchEvent(event);
+  assert_equals(shadowChild.parentNode, document.body);
+  assert_equals(event.target, document.body);
+  assert_equals(event.relatedTarget, host);
+  shadowChild.remove();
+}, "Retarget a shadow-tree relatedTarget, part 2");
+
+test(t => {
+  const event = new FocusEvent("heya", { relatedTarget: shadow, cancelable: true }),
+        callback = t.unreached_func();
+  host.addEventListener("heya", callback);
+  t.add_cleanup(() => host.removeEventListener("heya", callback));
+  event.preventDefault();
+  assert_true(event.defaultPrevented);
+  assert_false(host.dispatchEvent(event));
+  assert_equals(event.target, null);
+  assert_equals(event.relatedTarget, null);
+  // Check that the dispatch flag is cleared
+  event.initEvent("x");
+  assert_equals(event.type, "x");
+}, "Reset targets on early return");
+
+test(t => {
+  const input = document.body.appendChild(document.createElement("input")),
+        event = new MouseEvent("click", { relatedTarget: shadow });
+  let seen = false;
+  t.add_cleanup(() => input.remove());
+  input.type = "checkbox";
+  input.oninput = t.step_func(() => {
+    assert_equals(event.target, null);
+    assert_equals(event.relatedTarget, null);
+    assert_equals(event.composedPath().length, 0);
+    seen = true;
+  });
+  assert_true(input.dispatchEvent(event));
+  assert_true(seen);
+}, "Reset targets before activation behavior");
diff --git a/testing/web-platform/tests/dom/events/replace-event-listener-null-browsing-context-crash.html b/testing/web-platform/tests/dom/events/replace-event-listener-null-browsing-context-crash.html
new file mode 100644
index 0000000000..f41955eedd
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/replace-event-listener-null-browsing-context-crash.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<title>Event listeners: replace listener after moving between documents</title>
+<link rel="author" title="Nate Chapin" href="mailto:japhet@chromium.org">
+<link rel="help" href="https://w3c.github.io/touch-events/#dom-globaleventhandlers-ontouchcancel">
+<link rel="help" href="https://bugs.chromium.org/p/chromium/issues/detail?id=1083793">
+<meta name="assert" content="Overwriting an attribute event listener after adopting the owning node to a different document should not crash"/>
+<progress id="p">
+<iframe id="i"></iframe>
+<script>
+var p = document.getElementById("p");
+i.contentDocument.adoptNode(p);
+p.setAttribute("ontouchcancel", "");
+document.body.appendChild(p);
+p.setAttribute("ontouchcancel", "");
+</script>
+
diff --git a/testing/web-platform/tests/dom/events/resources/empty-document.html b/testing/web-platform/tests/dom/events/resources/empty-document.html
new file mode 100644
index 0000000000..b9cd130a07
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/resources/empty-document.html
@@ -0,0 +1,3 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<body>
diff --git a/testing/web-platform/tests/dom/events/resources/event-global-extra-frame.html b/testing/web-platform/tests/dom/events/resources/event-global-extra-frame.html
new file mode 100644
index 0000000000..241dda8b66
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/resources/event-global-extra-frame.html
@@ -0,0 +1,9 @@
+<script>
+function listener(e) {
+  parent.frameState = {
+    event: e,
+    windowEvent: window.event,
+    parentEvent: parent.event
+  }
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/resources/event-global-is-still-set-when-coercing-beforeunload-result-frame.html b/testing/web-platform/tests/dom/events/resources/event-global-is-still-set-when-coercing-beforeunload-result-frame.html
new file mode 100644
index 0000000000..5df4fa2793
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/resources/event-global-is-still-set-when-coercing-beforeunload-result-frame.html
@@ -0,0 +1,6 @@
+<!doctype html>
+<meta charset="utf-8">
+<body>
+<script>
+window.onbeforeunload = () => ({ toString: () => { parent.currentEventInToString = window.event; } });
+</script>
diff --git a/testing/web-platform/tests/dom/events/resources/prefixed-animation-event-tests.js b/testing/web-platform/tests/dom/events/resources/prefixed-animation-event-tests.js
new file mode 100644
index 0000000000..021b6bb9df
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/resources/prefixed-animation-event-tests.js
@@ -0,0 +1,366 @@
+'use strict'
+
+// Runs a set of tests for a given prefixed/unprefixed animation event (e.g.
+// animationstart/webkitAnimationStart).
+//
+// The eventDetails object must have the following form:
+// {
+//   isTransition: false, <-- can be omitted, default false
+//   unprefixedType: 'animationstart',
+//   prefixedType: 'webkitAnimationStart',
+//   animationCssStyle: '1ms',  <-- must NOT include animation name or
+//                                  transition property
+// }
+function runAnimationEventTests(eventDetails) {
+  const {
+    isTransition,
+    unprefixedType,
+    prefixedType,
+    animationCssStyle
+  } = eventDetails;
+
+  // Derive the DOM event handler names, e.g. onanimationstart.
+  const unprefixedHandler = `on${unprefixedType}`;
+  const prefixedHandler = `on${prefixedType.toLowerCase()}`;
+
+  const style = document.createElement('style');
+  document.head.appendChild(style);
+  if (isTransition) {
+    style.sheet.insertRule(
+      `.baseStyle { width: 100px; transition: width ${animationCssStyle}; }`);
+    style.sheet.insertRule('.transition { width: 200px !important; }');
+  } else {
+    style.sheet.insertRule('@keyframes anim {}');
+  }
+
+  function triggerAnimation(div) {
+    if (isTransition) {
+      div.classList.add('transition');
+    } else {
+      div.style.animation = `anim ${animationCssStyle}`;
+    }
+  }
+
+  test(t => {
+    const div = createDiv(t);
+
+    assert_equals(div[unprefixedHandler], null,
+        `${unprefixedHandler} should initially be null`);
+    assert_equals(div[prefixedHandler], null,
+        `${prefixedHandler} should initially be null`);
+
+    // Setting one should not affect the other.
+    div[unprefixedHandler] = () => { };
+
+    assert_not_equals(div[unprefixedHandler], null,
+        `setting ${unprefixedHandler} should make it non-null`);
+    assert_equals(div[prefixedHandler], null,
+        `setting ${unprefixedHandler} should not affect ${prefixedHandler}`);
+
+    div[prefixedHandler] = () => { };
+
+    assert_not_equals(div[prefixedHandler], null,
+        `setting ${prefixedHandler} should make it non-null`);
+    assert_not_equals(div[unprefixedHandler], div[prefixedHandler],
+        'the setters should be different');
+  }, `${unprefixedHandler} and ${prefixedHandler} are not aliases`);
+
+  // The below tests primarily test the interactions of prefixed animation
+  // events in the algorithm for invoking events:
+  // https://dom.spec.whatwg.org/#concept-event-listener-invoke
+
+  promise_test(async t => {
+    const div = createDiv(t);
+
+    let receivedEventCount = 0;
+    addTestScopedEventHandler(t, div, prefixedHandler, () => {
+      receivedEventCount++;
+    });
+    addTestScopedEventListener(t, div, prefixedType, () => {
+      receivedEventCount++;
+    });
+
+    // The HTML spec[0] specifies that the prefixed event handlers have an
+    // 'Event handler event type' of the appropriate prefixed event type. E.g.
+    // onwebkitanimationend creates a listener for the event type
+    // 'webkitAnimationEnd'.
+    //
+    // [0]: https://html.spec.whatwg.org/multipage/webappapis.html#event-handlers-on-elements,-document-objects,-and-window-objects
+    div.dispatchEvent(new AnimationEvent(prefixedType));
+    assert_equals(receivedEventCount, 2,
+                'prefixed listener and handler received event');
+  }, `dispatchEvent of a ${prefixedType} event does trigger a ` +
+      `prefixed event handler or listener`);
+
+  promise_test(async t => {
+    const div = createDiv(t);
+
+    let receivedEvent = false;
+    addTestScopedEventHandler(t, div, unprefixedHandler, () => {
+      receivedEvent = true;
+    });
+    addTestScopedEventListener(t, div, unprefixedType, () => {
+      receivedEvent = true;
+    });
+
+    div.dispatchEvent(new AnimationEvent(prefixedType));
+    assert_false(receivedEvent,
+                'prefixed listener or handler received event');
+  }, `dispatchEvent of a ${prefixedType} event does not trigger an ` +
+    `unprefixed event handler or listener`);
+
+
+  promise_test(async t => {
+    const div = createDiv(t);
+
+    let receivedEvent = false;
+    addTestScopedEventHandler(t, div, prefixedHandler, () => {
+      receivedEvent = true;
+    });
+    addTestScopedEventListener(t, div, prefixedType, () => {
+      receivedEvent = true;
+    });
+
+    // The rewrite rules from
+    // https://dom.spec.whatwg.org/#concept-event-listener-invoke step 8 do not
+    // apply because isTrusted will be false.
+    div.dispatchEvent(new AnimationEvent(unprefixedType));
+    assert_false(receivedEvent, 'prefixed listener or handler received event');
+  }, `dispatchEvent of an ${unprefixedType} event does not trigger a ` +
+      `prefixed event handler or listener`);
+
+  promise_test(async t => {
+    const div = createDiv(t);
+
+    let receivedEvent = false;
+    addTestScopedEventHandler(t, div, prefixedHandler, () => {
+      receivedEvent = true;
+    });
+
+    triggerAnimation(div);
+    await waitForEventThenAnimationFrame(t, unprefixedType);
+    assert_true(receivedEvent, `received ${prefixedHandler} event`);
+  }, `${prefixedHandler} event handler should trigger for an animation`);
+
+  promise_test(async t => {
+    const div = createDiv(t);
+
+    let receivedPrefixedEvent = false;
+    addTestScopedEventHandler(t, div, prefixedHandler, () => {
+      receivedPrefixedEvent = true;
+    });
+    let receivedUnprefixedEvent = false;
+    addTestScopedEventHandler(t, div, unprefixedHandler, () => {
+      receivedUnprefixedEvent = true;
+    });
+
+    triggerAnimation(div);
+    await waitForEventThenAnimationFrame(t, unprefixedType);
+    assert_true(receivedUnprefixedEvent, `received ${unprefixedHandler} event`);
+    assert_false(receivedPrefixedEvent, `received ${prefixedHandler} event`);
+  }, `${prefixedHandler} event handler should not trigger if an unprefixed ` +
+      `event handler also exists`);
+
+  promise_test(async t => {
+    const div = createDiv(t);
+
+    let receivedPrefixedEvent = false;
+    addTestScopedEventHandler(t, div, prefixedHandler, () => {
+      receivedPrefixedEvent = true;
+    });
+    let receivedUnprefixedEvent = false;
+    addTestScopedEventListener(t, div, unprefixedType, () => {
+      receivedUnprefixedEvent = true;
+    });
+
+    triggerAnimation(div);
+    await waitForEventThenAnimationFrame(t, unprefixedHandler);
+    assert_true(receivedUnprefixedEvent, `received ${unprefixedHandler} event`);
+    assert_false(receivedPrefixedEvent, `received ${prefixedHandler} event`);
+  }, `${prefixedHandler} event handler should not trigger if an unprefixed ` +
+      `listener also exists`);
+
+  promise_test(async t => {
+    // We use a parent/child relationship to be able to register both prefixed
+    // and unprefixed event handlers without the deduplication logic kicking in.
+    const parent = createDiv(t);
+    const child = createDiv(t);
+    parent.appendChild(child);
+    // After moving the child, we have to clean style again.
+    getComputedStyle(child).transition;
+    getComputedStyle(child).width;
+
+    let observedUnprefixedType;
+    addTestScopedEventHandler(t, parent, unprefixedHandler, e => {
+      observedUnprefixedType = e.type;
+    });
+    let observedPrefixedType;
+    addTestScopedEventHandler(t, child, prefixedHandler, e => {
+      observedPrefixedType = e.type;
+    });
+
+    triggerAnimation(child);
+    await waitForEventThenAnimationFrame(t, unprefixedType);
+
+    assert_equals(observedUnprefixedType, unprefixedType);
+    assert_equals(observedPrefixedType, prefixedType);
+  }, `event types for prefixed and unprefixed ${unprefixedType} event ` +
+    `handlers should be named appropriately`);
+
+  promise_test(async t => {
+    const div = createDiv(t);
+
+    let receivedEvent = false;
+    addTestScopedEventListener(t, div, prefixedType, () => {
+      receivedEvent = true;
+    });
+
+    triggerAnimation(div);
+    await waitForEventThenAnimationFrame(t, unprefixedHandler);
+    assert_true(receivedEvent, `received ${prefixedType} event`);
+  }, `${prefixedType} event listener should trigger for an animation`);
+
+  promise_test(async t => {
+    const div = createDiv(t);
+
+    let receivedPrefixedEvent = false;
+    addTestScopedEventListener(t, div, prefixedType, () => {
+      receivedPrefixedEvent = true;
+    });
+    let receivedUnprefixedEvent = false;
+    addTestScopedEventListener(t, div, unprefixedType, () => {
+      receivedUnprefixedEvent = true;
+    });
+
+    triggerAnimation(div);
+    await waitForEventThenAnimationFrame(t, unprefixedHandler);
+    assert_true(receivedUnprefixedEvent, `received ${unprefixedType} event`);
+    assert_false(receivedPrefixedEvent, `received ${prefixedType} event`);
+  }, `${prefixedType} event listener should not trigger if an unprefixed ` +
+      `listener also exists`);
+
+  promise_test(async t => {
+    const div = createDiv(t);
+
+    let receivedPrefixedEvent = false;
+    addTestScopedEventListener(t, div, prefixedType, () => {
+      receivedPrefixedEvent = true;
+    });
+    let receivedUnprefixedEvent = false;
+    addTestScopedEventHandler(t, div, unprefixedHandler, () => {
+      receivedUnprefixedEvent = true;
+    });
+
+    triggerAnimation(div);
+    await waitForEventThenAnimationFrame(t, unprefixedHandler);
+    assert_true(receivedUnprefixedEvent, `received ${unprefixedType} event`);
+    assert_false(receivedPrefixedEvent, `received ${prefixedType} event`);
+  }, `${prefixedType} event listener should not trigger if an unprefixed ` +
+       `event handler also exists`);
+
+  promise_test(async t => {
+    // We use a parent/child relationship to be able to register both prefixed
+    // and unprefixed event listeners without the deduplication logic kicking in.
+    const parent = createDiv(t);
+    const child = createDiv(t);
+    parent.appendChild(child);
+    // After moving the child, we have to clean style again.
+    getComputedStyle(child).transition;
+    getComputedStyle(child).width;
+
+    let observedUnprefixedType;
+    addTestScopedEventListener(t, parent, unprefixedType, e => {
+      observedUnprefixedType = e.type;
+    });
+    let observedPrefixedType;
+    addTestScopedEventListener(t, child, prefixedType, e => {
+      observedPrefixedType = e.type;
+    });
+
+    triggerAnimation(child);
+    await waitForEventThenAnimationFrame(t, unprefixedHandler);
+
+    assert_equals(observedUnprefixedType, unprefixedType);
+    assert_equals(observedPrefixedType, prefixedType);
+  }, `event types for prefixed and unprefixed ${unprefixedType} event ` +
+      `listeners should be named appropriately`);
+
+  promise_test(async t => {
+    const div = createDiv(t);
+
+    let receivedEvent = false;
+    addTestScopedEventListener(t, div, prefixedType.toLowerCase(), () => {
+      receivedEvent = true;
+    });
+    addTestScopedEventListener(t, div, prefixedType.toUpperCase(), () => {
+      receivedEvent = true;
+    });
+
+    triggerAnimation(div);
+    await waitForEventThenAnimationFrame(t, unprefixedHandler);
+    assert_false(receivedEvent, `received ${prefixedType} event`);
+  }, `${prefixedType} event listener is case sensitive`);
+}
+
+// Below are utility functions.
+
+// Creates a div element, appends it to the document body and removes the
+// created element during test cleanup.
+function createDiv(test) {
+  const element = document.createElement('div');
+  element.classList.add('baseStyle');
+  document.body.appendChild(element);
+  test.add_cleanup(() => {
+    element.remove();
+  });
+
+  // Flush style before returning. Some browsers only do partial style re-calc,
+  // so ask for all important properties to make sure they are applied.
+  getComputedStyle(element).transition;
+  getComputedStyle(element).width;
+
+  return element;
+}
+
+// Adds an event handler for |handlerName| (calling |callback|) to the given
+// |target|, that will automatically be cleaned up at the end of the test.
+function addTestScopedEventHandler(test, target, handlerName, callback) {
+  assert_regexp_match(
+      handlerName, /^on/, 'Event handler names must start with "on"');
+  assert_equals(target[handlerName], null,
+                `${handlerName} must be supported and not previously set`);
+  target[handlerName] = callback;
+  // We need this cleaned up even if the event handler doesn't run.
+  test.add_cleanup(() => {
+    if (target[handlerName])
+      target[handlerName] = null;
+  });
+}
+
+// Adds an event listener for |type| (calling |callback|) to the given
+// |target|, that will automatically be cleaned up at the end of the test.
+function addTestScopedEventListener(test, target, type, callback) {
+  target.addEventListener(type, callback);
+  // We need this cleaned up even if the event handler doesn't run.
+  test.add_cleanup(() => {
+    target.removeEventListener(type, callback);
+  });
+}
+
+// Returns a promise that will resolve once the passed event (|eventName|) has
+// triggered and one more animation frame has happened. Automatically chooses
+// between an event handler or event listener based on whether |eventName|
+// begins with 'on'.
+//
+// We always listen on window as we don't want to interfere with the test via
+// triggering the prefixed event deduplication logic.
+function waitForEventThenAnimationFrame(test, eventName) {
+  return new Promise((resolve, _) => {
+    const eventFunc = eventName.startsWith('on')
+        ? addTestScopedEventHandler : addTestScopedEventListener;
+    eventFunc(test, window, eventName, () => {
+      // rAF once to give the event under test time to come through.
+      requestAnimationFrame(resolve);
+    });
+  });
+}
diff --git a/testing/web-platform/tests/dom/events/scrolling/iframe-chains.html b/testing/web-platform/tests/dom/events/scrolling/iframe-chains.html
new file mode 100644
index 0000000000..fb7d674aae
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/iframe-chains.html
@@ -0,0 +1,48 @@
+<!DOCTYPE html>
+<html>
+<head>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<style>
+
+body { margin: 0; padding: 10px; }
+.space { height: 2000px; }
+
+#scroller {
+  border: 3px solid green;
+  position: absolute;
+  z-index: 0;
+  overflow: auto;
+  padding: 10px;
+  width: 250px;
+  height: 150px;
+}
+
+.ifr {
+  border: 3px solid blue;
+  width: 200px;
+  height: 100px;
+}
+
+</style>
+</head>
+<body>
+<div id=scroller>
+  <iframe srcdoc="SCROLL ME" class=ifr></iframe>
+  <div class=space></div>
+</div>
+<div class=space></div>
+<script>
+
+promise_test(async t => {
+  await new test_driver.Actions().scroll(50, 50, 0, 50).send();
+  // Allow the possibility the scroll is not fully synchronous
+  await t.step_wait(() => scroller.scrollTop === 50);
+}, "Wheel scroll in iframe chains to containing element.");
+
+</script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/dom/events/scrolling/input-text-scroll-event-when-using-arrow-keys.html b/testing/web-platform/tests/dom/events/scrolling/input-text-scroll-event-when-using-arrow-keys.html
new file mode 100644
index 0000000000..f84e446527
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/input-text-scroll-event-when-using-arrow-keys.html
@@ -0,0 +1,71 @@
+<!doctype html>
+<html>
+<head>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+
+</head>
+<body onload=runTest()>
+    <p>Moving the cursor using the arrow keys into an
+        input element fires scroll events when text has to scroll into view.
+        Uses arrow keys to move forward and backwards in the input
+        element.</p>
+    <input type="text" style='width: 50px'
+    value="Fooooooooooooooooooooooooooooooooooooooooooooooooo"/>
+    <textarea rows="4" cols="4">
+        Fooooooooooooooooooooooooooooooooooooooooooooooooo
+    </textarea>
+
+    <script>
+      async function moveCursorRightInsideElement(element, value){
+          var arrowRight = '\uE014';
+          for(var i=0;i<value;i++){
+            await test_driver.send_keys(element, arrowRight);
+          }
+      }
+
+      function runTest(){
+          promise_test(async(t) => { return new Promise(async (resolve, reject) => {
+            var input = document.getElementsByTagName('input')[0];
+            function handleScroll(){
+              resolve("Scroll Event successfully fired!");
+            }
+            input.addEventListener('scroll', handleScroll, false);
+            // move cursor to the right until the text scrolls
+            while(input.scrollLeft === 0){
+              await moveCursorRightInsideElement(input, 1);
+            }
+            // if there is no scroll event fired then test will fail by timeout
+          })},
+             /*
+               Moving the cursor using the arrow keys into an input element
+               fires scroll events when text has to scroll into view.
+               Uses arrow keys to move right in the input element.
+             */
+           "Scroll event fired for <input> element.");
+
+          promise_test(async(t) => { return new Promise(async (resolve, reject) => {
+            var textarea = document.getElementsByTagName('textarea')[0];
+            function handleScroll(){
+              resolve("Scroll Event successfully fired!");
+            }
+            textarea.addEventListener('scroll', handleScroll, false);
+            // move cursor to the right until the text scrolls
+            while(textarea.scrollLeft === 0){
+              await moveCursorRightInsideElement(textarea, 1);
+            }
+            // if there is no scroll event fired then test will fail by timeout
+          })},
+             /*
+              Moving the cursor using the arrow keys into a textarea element
+              fires scroll events when text has to scroll into view.
+              Uses arrow keys to move right in the textarea element.
+            */
+              "Scroll event fired for <textarea> element.");
+      }
+    </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/dom/events/scrolling/overscroll-deltas.html b/testing/web-platform/tests/dom/events/scrolling/overscroll-deltas.html
new file mode 100644
index 0000000000..6f0b77f22e
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/overscroll-deltas.html
@@ -0,0 +1,85 @@
+<!DOCTYPE HTML>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+#targetDiv {
+  width: 500px;
+  height: 500px;
+  background: red;
+}
+html, body {
+  /* Prevent any built-in browser overscroll features from consuming the scroll
+   * deltas */
+  overscroll-behavior: none;
+}
+
+</style>
+
+<body style="margin:0;" onload=runTest()>
+<div id="targetDiv">
+</div>
+</body>
+
+<script>
+var target_div = document.getElementById('targetDiv');
+var overscrolled_x_deltas = [];
+var overscrolled_y_deltas = [];
+var scrollend_received = false;
+
+function onOverscroll(event) {
+  overscrolled_x_deltas.push(event.deltaX);
+  overscrolled_y_deltas.push(event.deltaY);
+}
+
+function onScrollend(event) {
+  scrollend_received = true;
+}
+
+document.addEventListener("overscroll", onOverscroll);
+document.addEventListener("scrollend", onScrollend);
+
+function runTest() {
+  promise_test (async (t) => {
+    await waitForCompositorCommit();
+
+    // Scroll up on target div and wait for the doc to get overscroll event.
+    await touchScrollInTarget(300, target_div, 'up');
+    await waitFor(() => { return scrollend_received; },
+        'Document did not receive scrollend event.');
+
+    // Even though we request 300 pixels of scroll, the API above doesn't
+    // guarantee how much scroll delta will be generated - different browsers
+    // can consume different amounts for "touch slop" (for example). Ensure the
+    // overscroll reaches at least 100 pixels which is a fairly conservative
+    // value.
+    assert_greater_than(overscrolled_y_deltas.length, 0, "There should be at least one overscroll events when overscrolling.");
+    assert_equals(overscrolled_x_deltas.filter(function(x){ return x!=0; }).length, 0, "The deltaX attribute must be 0 when there is no scrolling in x direction.");
+    assert_less_than_equal(Math.max(...overscrolled_y_deltas), 0, "The deltaY attribute must be <= 0 when there is overscrolling in up direction.");
+    assert_less_than_equal(Math.min(...overscrolled_y_deltas),-100, "The deltaY attribute must be the number of pixels overscrolled.");
+
+    await waitForCompositorCommit();
+    overscrolled_x_deltas = [];
+    overscrolled_y_deltas = [];
+    scrollend_received = false;
+
+    // Scroll left on target div and wait for the doc to get overscroll event.
+    await touchScrollInTarget(300, target_div, 'left');
+    await waitFor(() => { return scrollend_received; },
+        'Document did not receive scrollend event.');
+
+    // TODO(bokan): It looks like Chrome inappropriately filters some scroll
+    // events despite |overscroll-behavior| being set to none. The overscroll
+    // amount here has been loosened but this should be fixed in Chrome.
+    // https://crbug.com/1112183.
+    assert_greater_than(overscrolled_y_deltas.length, 0, "There should be at least one overscroll events when overscrolling.");
+    assert_equals(overscrolled_y_deltas.filter(function(x){ return x!=0; }).length, 0, "The deltaY attribute must be 0 when there is no scrolling in y direction.");
+    assert_less_than_equal(Math.max(...overscrolled_x_deltas), 0, "The deltaX attribute must be <= 0 when there is overscrolling in left direction.");
+    assert_less_than_equal(Math.min(...overscrolled_x_deltas),-50, "The deltaX attribute must be the number of pixels overscrolled.");
+
+  }, 'Tests that the document gets overscroll event with right deltaX/Y attributes.');
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/scrolling/overscroll-event-fired-to-document.html b/testing/web-platform/tests/dom/events/scrolling/overscroll-event-fired-to-document.html
new file mode 100644
index 0000000000..c054ffca9c
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/overscroll-event-fired-to-document.html
@@ -0,0 +1,62 @@
+<!DOCTYPE HTML>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+#targetDiv {
+  width: 200px;
+  height: 200px;
+  overflow: scroll;
+}
+
+#innerDiv {
+  width: 400px;
+  height: 400px;
+}
+</style>
+
+<body style="margin:0" onload=runTest()>
+<div id="targetDiv">
+  <div id="innerDiv">
+  </div>
+</div>
+</body>
+
+<script>
+var target_div = document.getElementById('targetDiv');
+var overscrolled_x_delta = 0;
+var overscrolled_y_delta = 0;
+function onOverscroll(event) {
+  assert_false(event.cancelable);
+  // overscroll events are bubbled when the target node is document.
+  assert_true(event.bubbles);
+  overscrolled_x_delta = event.deltaX;
+  overscrolled_y_delta = event.deltaY;
+}
+document.addEventListener("overscroll", onOverscroll);
+
+function runTest() {
+  promise_test (async (t) => {
+    // Make sure that no overscroll event is sent to target_div.
+    target_div.addEventListener("overscroll",
+        t.unreached_func("target_div got unexpected overscroll event."));
+    await waitForCompositorCommit();
+
+    // Scroll up on target div and wait for the doc to get overscroll event.
+    await touchScrollInTarget(300, target_div, 'up');
+    await waitFor(() => { return overscrolled_y_delta < 0; },
+        'Document did not receive overscroll event after scroll up on target.');
+    assert_equals(target_div.scrollTop, 0);
+
+    // Scroll left on target div and wait for the doc to get overscroll event.
+    await touchScrollInTarget(300, target_div, 'left');
+    await waitFor(() => { return overscrolled_x_delta < 0; },
+        'Document did not receive overscroll event after scroll left on target.');
+    assert_equals(target_div.scrollLeft, 0);
+  }, 'Tests that the document gets overscroll event when no element scrolls ' +
+      'after touch scrolling.');
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/scrolling/overscroll-event-fired-to-element-with-overscroll-behavior.html b/testing/web-platform/tests/dom/events/scrolling/overscroll-event-fired-to-element-with-overscroll-behavior.html
new file mode 100644
index 0000000000..750080e656
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/overscroll-event-fired-to-element-with-overscroll-behavior.html
@@ -0,0 +1,92 @@
+<!DOCTYPE HTML>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+#overscrollXDiv {
+  width: 600px;
+  height: 600px;
+  overflow: scroll;
+  overscroll-behavior-x: contain;
+}
+#overscrollYDiv {
+  width: 500px;
+  height: 500px;
+  overflow: scroll;
+  overscroll-behavior-y: none;
+}
+#targetDiv {
+  width: 400px;
+  height: 400px;
+  overflow: scroll;
+}
+.content {
+  width:800px;
+  height:800px;
+}
+</style>
+
+<body style="margin:0" onload=runTest()>
+<div id="overscrollXDiv">
+  <div class=content>
+    <div id="overscrollYDiv">
+      <div class=content>
+        <div id="targetDiv">
+          <div class="content">
+          </div>
+        </div>
+      </div>
+    </div>
+  </div>
+</div>
+</body>
+
+<script>
+var target_div = document.getElementById('targetDiv');
+var overscrolled_x_delta = 0;
+var overscrolled_y_delta = 0;
+function onOverscrollX(event) {
+  assert_false(event.cancelable);
+  assert_false(event.bubbles);
+  overscrolled_x_delta = event.deltaX;
+}
+function onOverscrollY(event) {
+  assert_false(event.cancelable);
+  assert_false(event.bubbles);
+  overscrolled_y_delta = event.deltaY;
+}
+// Test that both "onoverscroll" and addEventListener("overscroll"... work.
+document.getElementById('overscrollXDiv').onoverscroll = onOverscrollX;
+document.getElementById('overscrollYDiv').
+    addEventListener("overscroll", onOverscrollY);
+
+function runTest() {
+  promise_test (async (t) => {
+    // Make sure that no overscroll event is sent to document or target_div.
+    document.addEventListener("overscroll",
+        t.unreached_func("Document got unexpected overscroll event."));
+    target_div.addEventListener("overscroll",
+        t.unreached_func("target_div got unexpected overscroll event."));
+    await waitForCompositorCommit();
+    // Scroll up on target div and wait for the element with overscroll-y to get
+    // overscroll event.
+    await touchScrollInTarget(300, target_div, 'up');
+    await waitFor(() => { return overscrolled_y_delta < 0; },
+        'Expected element did not receive overscroll event after scroll up on ' +
+        'target.');
+    assert_equals(target_div.scrollTop, 0);
+
+    // Scroll left on target div and wait for the element with overscroll-x to
+    // get overscroll event.
+    await touchScrollInTarget(300, target_div, 'left');
+    await waitFor(() => { return overscrolled_x_delta < 0; },
+        'Expected element did not receive overscroll event after scroll left ' +
+        'on target.');
+    assert_equals(target_div.scrollLeft, 0);
+  }, 'Tests that the last element in the cut scroll chain gets overscroll ' +
+     'event when no element scrolls by touch.');
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/scrolling/overscroll-event-fired-to-scrolled-element.html b/testing/web-platform/tests/dom/events/scrolling/overscroll-event-fired-to-scrolled-element.html
new file mode 100644
index 0000000000..cfc782a809
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/overscroll-event-fired-to-scrolled-element.html
@@ -0,0 +1,65 @@
+<!DOCTYPE HTML>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+#scrollableDiv {
+  width: 200px;
+  height: 200px;
+  overflow: scroll;
+}
+
+#innerDiv {
+  width: 400px;
+  height: 400px;
+}
+</style>
+
+<body style="margin:0" onload=runTest()>
+<div id="scrollableDiv">
+  <div id="innerDiv">
+  </div>
+</div>
+</body>
+
+<script>
+var scrolling_div = document.getElementById('scrollableDiv');
+var overscrolled_x_delta = 0;
+var overscrolled_y_delta = 0;
+function onOverscroll(event) {
+  assert_false(event.cancelable);
+  assert_false(event.bubbles);
+  overscrolled_x_delta = event.deltaX;
+  overscrolled_y_delta = event.deltaY;
+}
+scrolling_div.addEventListener("overscroll", onOverscroll);
+
+function runTest() {
+  promise_test (async (t) => {
+    // Make sure that no overscroll event is sent to document.
+    document.addEventListener("overscroll",
+        t.unreached_func("Document got unexpected overscroll event."));
+    await waitForCompositorCommit();
+
+    // Do a horizontal scroll and wait for overscroll event.
+    await touchScrollInTarget(300, scrolling_div , 'right');
+    await waitFor(() => { return overscrolled_x_delta > 0; },
+        'Scroller did not receive overscroll event after horizontal scroll.');
+    assert_equals(scrolling_div.scrollWidth - scrolling_div.scrollLeft,
+                scrolling_div.clientWidth);
+
+    overscrolled_x_delta = 0;
+    overscrolled_y_delta = 0;
+
+    // Do a vertical scroll and wait for overscroll event.
+    await touchScrollInTarget(300, scrolling_div, 'down');
+    await waitFor(() => { return overscrolled_y_delta > 0; },
+        'Scroller did not receive overscroll event after vertical scroll.');
+    assert_equals(scrolling_div.scrollHeight - scrolling_div.scrollTop,
+                scrolling_div.clientHeight);
+  }, 'Tests that the scrolled element gets overscroll event after fully scrolling by touch.');
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/scrolling/overscroll-event-fired-to-window.html b/testing/web-platform/tests/dom/events/scrolling/overscroll-event-fired-to-window.html
new file mode 100644
index 0000000000..ef5ae3daef
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/overscroll-event-fired-to-window.html
@@ -0,0 +1,52 @@
+<!DOCTYPE HTML>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+#targetDiv {
+  width: 200px;
+  height: 200px;
+  overflow: scroll;
+}
+
+#innerDiv {
+  width: 400px;
+  height: 400px;
+}
+</style>
+
+<body style="margin:0" onload=runTest()>
+<div id="targetDiv">
+  <div id="innerDiv">
+  </div>
+</div>
+</body>
+
+<script>
+var target_div = document.getElementById('targetDiv');
+var window_received_overscroll = false;
+
+function onOverscroll(event) {
+  assert_false(event.cancelable);
+  // overscroll events targetting document are bubbled to the window.
+  assert_true(event.bubbles);
+  window_received_overscroll = true;
+}
+window.addEventListener("overscroll", onOverscroll);
+
+function runTest() {
+  promise_test (async (t) => {
+    // Make sure that no overscroll event is sent to target_div.
+    target_div.addEventListener("overscroll",
+        t.unreached_func("target_div got unexpected overscroll event."));
+    // Scroll up on target div and wait for the window to get overscroll event.
+    await touchScrollInTarget(300, target_div, 'up');
+    await waitFor(() => { return window_received_overscroll; },
+        'Window did not receive overscroll event after scroll up on target.');
+  }, 'Tests that the window gets overscroll event when no element scrolls' +
+     'after touch scrolling.');
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/scrolling/scroll_support.js b/testing/web-platform/tests/dom/events/scrolling/scroll_support.js
new file mode 100644
index 0000000000..169393e4c3
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/scroll_support.js
@@ -0,0 +1,163 @@
+async function waitForScrollendEvent(test, target, timeoutMs = 500) {
+  return new Promise((resolve, reject) => {
+    const timeoutCallback = test.step_timeout(() => {
+      reject(`No Scrollend event received for target ${target}`);
+    }, timeoutMs);
+    target.addEventListener('scrollend', (evt) => {
+      clearTimeout(timeoutCallback);
+      resolve(evt);
+    }, { once: true });
+  });
+}
+
+const MAX_FRAME = 700;
+const MAX_UNCHANGED_FRAMES = 20;
+
+// Returns a promise that resolves when the given condition is met or rejects
+// after MAX_FRAME animation frames.
+// TODO(crbug.com/1400399): deprecate. We should not use frame based waits in
+// WPT as frame rates may vary greatly in different testing environments.
+function waitFor(condition, error_message = 'Reaches the maximum frames.') {
+  return new Promise((resolve, reject) => {
+    function tick(frames) {
+      // We requestAnimationFrame either for MAX_FRAM frames or until condition
+      // is met.
+      if (frames >= MAX_FRAME)
+        reject(error_message);
+      else if (condition())
+        resolve();
+      else
+        requestAnimationFrame(tick.bind(this, frames + 1));
+    }
+    tick(0);
+  });
+}
+
+// TODO(crbug.com/1400446): Test driver should defer sending events until the
+// browser is ready. Also the term compositor-commit is misleading as not all
+// user-agents use a compositor process.
+function waitForCompositorCommit() {
+  return new Promise((resolve) => {
+    // rAF twice.
+    window.requestAnimationFrame(() => {
+      window.requestAnimationFrame(resolve);
+    });
+  });
+}
+
+// TODO(crbug.com/1400399): Deprecate as frame rates may vary greatly in
+// different test environments.
+function waitForAnimationEnd(getValue) {
+  var last_changed_frame = 0;
+  var last_position = getValue();
+  return new Promise((resolve, reject) => {
+    function tick(frames) {
+    // We requestAnimationFrame either for MAX_FRAME or until
+    // MAX_UNCHANGED_FRAMES with no change have been observed.
+      if (frames >= MAX_FRAME || frames - last_changed_frame > MAX_UNCHANGED_FRAMES) {
+        resolve();
+      } else {
+        current_value = getValue();
+        if (last_position != current_value) {
+          last_changed_frame = frames;
+          last_position = current_value;
+        }
+        requestAnimationFrame(tick.bind(this, frames + 1));
+      }
+    }
+    tick(0);
+  })
+}
+
+// Scrolls in target according to move_path with pauses in between
+function touchScrollInTargetSequentiallyWithPause(target, move_path, pause_time_in_ms = 100) {
+  const test_driver_actions = new test_driver.Actions()
+    .addPointer("pointer1", "touch")
+    .pointerMove(0, 0, {origin: target})
+    .pointerDown();
+
+  const substeps = 5;
+  let x = 0;
+  let y = 0;
+  // Do each move in 5 steps
+  for(let move of move_path) {
+    let step_x = (move.x - x) / substeps;
+    let step_y = (move.y - y) / substeps;
+    for(let step = 0; step < substeps; step++) {
+      x += step_x;
+      y += step_y;
+      test_driver_actions.pointerMove(x, y, {origin: target});
+    }
+    test_driver_actions.pause(pause_time_in_ms);
+  }
+
+  return test_driver_actions.pointerUp().send();
+}
+
+function touchScrollInTarget(pixels_to_scroll, target, direction, pause_time_in_ms = 100) {
+  var x_delta = 0;
+  var y_delta = 0;
+  const num_movs = 5;
+  if (direction == "down") {
+    y_delta = -1 * pixels_to_scroll / num_movs;
+  } else if (direction == "up") {
+    y_delta = pixels_to_scroll / num_movs;
+  } else if (direction == "right") {
+    x_delta = -1 * pixels_to_scroll / num_movs;
+  } else if (direction == "left") {
+    x_delta = pixels_to_scroll / num_movs;
+  } else {
+    throw("scroll direction '" + direction + "' is not expected, direction should be 'down', 'up', 'left' or 'right'");
+  }
+  return new test_driver.Actions()
+      .addPointer("pointer1", "touch")
+      .pointerMove(0, 0, {origin: target})
+      .pointerDown()
+      .pointerMove(x_delta, y_delta, {origin: target})
+      .pointerMove(2 * x_delta, 2 * y_delta, {origin: target})
+      .pointerMove(3 * x_delta, 3 * y_delta, {origin: target})
+      .pointerMove(4 * x_delta, 4 * y_delta, {origin: target})
+      .pointerMove(5 * x_delta, 5 * y_delta, {origin: target})
+      .pause(pause_time_in_ms)
+      .pointerUp()
+      .send();
+}
+
+// Trigger fling by doing pointerUp right after pointerMoves.
+function touchFlingInTarget(pixels_to_scroll, target, direction) {
+  touchScrollInTarget(pixels_to_scroll, target, direction, 0 /* pause_time */);
+}
+
+function mouseActionsInTarget(target, origin, delta, pause_time_in_ms = 100) {
+  return new test_driver.Actions()
+    .addPointer("pointer1", "mouse")
+    .pointerMove(origin.x, origin.y, { origin: target })
+    .pointerDown()
+    .pointerMove(origin.x + delta.x, origin.y + delta.y, { origin: target })
+    .pointerMove(origin.x + delta.x * 2, origin.y + delta.y * 2, { origin: target })
+    .pause(pause_time_in_ms)
+    .pointerUp()
+    .send();
+}
+
+// Returns a promise that resolves when the given condition holds for 10
+// animation frames or rejects if the condition changes to false within 10
+// animation frames.
+// TODO(crbug.com/1400399): Deprecate as frame rates may very greatly in
+// different test environments.
+function conditionHolds(condition, error_message = 'Condition is not true anymore.') {
+  const MAX_FRAME = 10;
+  return new Promise((resolve, reject) => {
+    function tick(frames) {
+      // We requestAnimationFrame either for 10 frames or until condition is
+      // violated.
+      if (frames >= MAX_FRAME)
+        resolve();
+      else if (!condition())
+        reject(error_message);
+      else
+        requestAnimationFrame(tick.bind(this, frames + 1));
+    }
+    tick(0);
+  });
+}
diff --git a/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-after-sequence-of-scrolls.tentative.html b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-after-sequence-of-scrolls.tentative.html
new file mode 100644
index 0000000000..77bf029ced
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-after-sequence-of-scrolls.tentative.html
@@ -0,0 +1,63 @@
+<!DOCTYPE HTML>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+#targetDiv {
+  width: 200px;
+  height: 200px;
+  overflow: scroll;
+}
+
+#innerDiv {
+  width: 500px;
+  height: 4000px;
+}
+</style>
+
+<body style="margin:0" onload=runTest()>
+<div id="targetDiv">
+  <div id="innerDiv">
+  </div>
+</div>
+</body>
+
+<script>
+const target_div = document.getElementById('targetDiv');
+let scrollend_arrived = false;
+let scrollend_event_count = 0;
+
+function onScrollEnd(event) {
+  assert_false(event.cancelable);
+  assert_false(event.bubbles);
+  scrollend_arrived = true;
+  scrollend_event_count += 1;
+}
+
+function runTest() {
+  promise_test (async (t) => {
+    // Make sure that no scrollend event is sent to document.
+    document.addEventListener("scrollend",
+        t.unreached_func("document got unexpected scrollend event."));
+    await waitForCompositorCommit();
+
+    // Scroll down & up & down on target div and wait for the target_div to get scrollend event.
+    target_div.addEventListener("scrollend", onScrollEnd);
+    const move_path = [
+      { x: 0, y: -300}, // down
+      { x: 0, y: -100}, // up
+      { x: 0, y: -400}, // down
+      { x: 0, y: -200}, // up
+    ];
+    await touchScrollInTargetSequentiallyWithPause(target_div, move_path, 150);
+
+    await waitFor(() => {return scrollend_arrived;},
+        'target_div did not receive scrollend event after sequence of scrolls on target.');
+    assert_equals(scrollend_event_count, 1);
+  }, "Move down, up and down again, receive scrollend event only once");
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-after-snap.html b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-after-snap.html
new file mode 100644
index 0000000000..03079ddc6c
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-after-snap.html
@@ -0,0 +1,87 @@
+<!DOCTYPE html>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+div {
+  position: absolute;
+}
+#scroller {
+  width: 500px;
+  height: 500px;
+  overflow: scroll;
+  scroll-snap-type: both mandatory;
+  border: solid black 5px;
+}
+#space {
+  width: 2000px;
+  height: 2000px;
+}
+.target {
+  width: 200px;
+  height: 200px;
+  scroll-snap-align: start;
+  background-color: blue;
+}
+</style>
+
+<body style="margin:0" onload=runTests()>
+  <div id="scroller">
+    <div id="space"></div>
+    <div class="target" style="left: 0px; top: 0px;"></div>
+    <div class="target" style="left: 80px; top: 80px;"></div>
+    <div class="target" style="left: 200px; top: 200px;"></div>
+  </div>
+</body>
+
+<script>
+var scroller = document.getElementById("scroller");
+var space = document.getElementById("space");
+const MAX_FRAME_COUNT = 700;
+const MAX_UNCHANGED_FRAME = 20;
+
+function scrollTop() {
+  return scroller.scrollTop;
+}
+
+var scroll_arrived_after_scroll_end = false;
+var scroll_end_arrived = false;
+scroller.addEventListener("scroll", () => {
+  if (scroll_end_arrived)
+    scroll_arrived_after_scroll_end = true;
+});
+scroller.addEventListener("scrollend", () => {
+  scroll_end_arrived = true;
+});
+
+function runTests() {
+  promise_test (async () => {
+    await waitForCompositorCommit();
+    await touchScrollInTarget(100, scroller, 'down');
+    // Wait for the scroll snap animation to finish.
+    await waitForAnimationEnd(scrollTop);
+    await waitFor(() => { return scroll_end_arrived; });
+    // Verify that scroll snap animation has finished before firing scrollend event.
+    assert_false(scroll_arrived_after_scroll_end);
+  }, "Tests that scrollend is fired after scroll snap animation completion.");
+
+  promise_test (async () => {
+    // Reset scroll state.
+    scroller.scrollTo(0, 0);
+    await waitForCompositorCommit();
+    scroll_end_arrived = false;
+    scroll_arrived_after_scroll_end = false;
+
+    await touchFlingInTarget(50, scroller, 'down');
+    // Wait for the scroll snap animation to finish.
+    await waitForAnimationEnd(scrollTop);
+    await waitFor(() => { return scroll_end_arrived; });
+    // Verify that scroll snap animation has finished before firing scrollend event.
+    assert_false(scroll_arrived_after_scroll_end);
+  }, "Tests that scrollend is fired after fling snap animation completion.");
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-for-programmatic-scroll.html b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-for-programmatic-scroll.html
new file mode 100644
index 0000000000..c6569e0beb
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-for-programmatic-scroll.html
@@ -0,0 +1,135 @@
+<!DOCTYPE HTML>
+<meta name="timeout" content="long">
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+html {
+  height: 3000px;
+  width: 3000px;
+}
+#targetDiv {
+  width: 200px;
+  height: 200px;
+  overflow: scroll;
+}
+
+#innerDiv {
+  width: 400px;
+  height: 400px;
+}
+</style>
+
+<body style="margin:0" onload=runTest()>
+<div id="targetDiv">
+  <div id="innerDiv">
+  </div>
+</div>
+</body>
+<script>
+var element_scrollend_arrived = false;
+var document_scrollend_arrived = false;
+
+function onElementScrollEnd(event) {
+  assert_false(event.cancelable);
+  assert_false(event.bubbles);
+  element_scrollend_arrived = true;
+}
+
+function onDocumentScrollEnd(event) {
+  assert_false(event.cancelable);
+  // scrollend events are bubbled when the target node is document.
+  assert_true(event.bubbles);
+  document_scrollend_arrived = true;
+}
+
+function callScrollFunction([scrollTarget, scrollFunction, args]) {
+  scrollTarget[scrollFunction](args);
+}
+
+function runTest() {
+  let root_element = document.scrollingElement;
+  let target_div = document.getElementById("targetDiv");
+
+  promise_test (async (t) => {
+    await waitForCompositorCommit();
+    target_div.addEventListener("scrollend", onElementScrollEnd);
+    document.addEventListener("scrollend", onDocumentScrollEnd);
+
+    let test_cases = [
+      [target_div, 200, 200, [target_div, "scrollTo", { top: 200, left: 200, behavior: "auto" }]],
+      [target_div, 0, 0, [target_div, "scrollTo", { top: 0, left: 0, behavior: "smooth" }]],
+      [root_element, 200, 200, [root_element, "scrollTo", { top: 200, left: 200, behavior: "auto" }]],
+      [root_element, 0, 0, [root_element, "scrollTo", { top: 0, left: 0, behavior: "smooth" }]],
+      [target_div, 200, 200, [target_div, "scrollBy", { top: 200, left: 200, behavior: "auto" }]],
+      [target_div, 0, 0, [target_div, "scrollBy", { top: -200, left: -200, behavior: "smooth" }]],
+      [root_element, 200, 200, [root_element, "scrollBy", { top: 200, left: 200, behavior: "auto" }]],
+      [root_element, 0, 0, [root_element, "scrollBy", { top: -200, left: -200, behavior: "smooth" }]]
+    ];
+
+    for(i = 0; i < test_cases.length; i++) {
+      let t = test_cases[i];
+      let target = t[0];
+      let expected_x = t[1];
+      let expected_y = t[2];
+      let scroll_datas = t[3];
+
+      callScrollFunction(scroll_datas);
+      await waitFor(() => { return element_scrollend_arrived || document_scrollend_arrived; }, target.tagName + "." + scroll_datas[1] + " did not receive scrollend event.");
+      if (target == root_element)
+        assert_false(element_scrollend_arrived);
+      else
+        assert_false(document_scrollend_arrived);
+      assert_equals(target.scrollLeft, expected_x, target.tagName + "." + scroll_datas[1] + " scrollLeft");
+      assert_equals(target.scrollTop, expected_y, target.tagName + "." + scroll_datas[1] + " scrollTop");
+
+      element_scrollend_arrived = false;
+      document_scrollend_arrived = false;
+    }
+  }, "Tests scrollend event for calling scroll functions.");
+
+  promise_test(async (t) => {
+    await waitForCompositorCommit();
+
+    let test_cases = [
+      [target_div, "scrollTop"],
+      [target_div, "scrollLeft"],
+      [root_element, "scrollTop"],
+      [root_element, "scrollLeft"]
+    ];
+    for (i = 0; i < test_cases.length; i++) {
+      let t = test_cases[i];
+      let target = t[0];
+      let attribute = t[1];
+      let position = 200;
+
+      target.style.scrollBehavior = "smooth";
+      target[attribute] = position;
+      await waitFor(() => { return element_scrollend_arrived || document_scrollend_arrived; }, target.tagName + "." + attribute + " did not receive scrollend event.");
+      if (target == root_element)
+        assert_false(element_scrollend_arrived);
+      else
+        assert_false(document_scrollend_arrived);
+      assert_equals(target[attribute], position, target.tagName + "." + attribute + " ");
+      element_scrollend_arrived = false;
+      document_scrollend_arrived = false;
+
+      await waitForCompositorCommit();
+      target.style.scrollBehavior = "auto";
+      target[attribute] = 0;
+      await waitFor(() => { return element_scrollend_arrived || document_scrollend_arrived; }, target.tagName + "." + attribute + " did not receive scrollend event.");
+      if (target == root_element)
+        assert_false(element_scrollend_arrived);
+      else
+        assert_false(document_scrollend_arrived);
+      assert_equals(target[attribute], 0, target.tagName + "." + attribute + " ");
+      element_scrollend_arrived = false;
+      document_scrollend_arrived = false;
+    }
+  }, "Tests scrollend event for changing scroll attributes.");
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-for-scrollIntoView.html b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-for-scrollIntoView.html
new file mode 100644
index 0000000000..8782b1dfee
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-for-scrollIntoView.html
@@ -0,0 +1,124 @@
+<!DOCTYPE HTML>
+<meta name="timeout" content="long">
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+html {
+  height: 3000px;
+  width: 3000px;
+}
+#targetDiv {
+  width: 200px;
+  height: 200px;
+  overflow: scroll;
+}
+
+#innerDiv {
+  width: 400px;
+  height: 400px;
+}
+</style>
+
+<body style="margin:0" onload=runTest()>
+<div id="targetDiv">
+  <div id="innerDiv">
+  </div>
+</div>
+</body>
+<script>
+var element_scrollend_arrived = false;
+var document_scrollend_arrived = false;
+
+function onElementScrollEnd(event) {
+  assert_false(event.cancelable);
+  assert_false(event.bubbles);
+  element_scrollend_arrived = true;
+}
+
+function onDocumentScrollEnd(event) {
+  assert_false(event.cancelable);
+  // scrollend events are bubbled when the target node is document.
+  assert_true(event.bubbles);
+  document_scrollend_arrived = true;
+}
+
+function callScrollFunction([scrollTarget, scrollFunction, args]) {
+  scrollTarget[scrollFunction](args);
+}
+
+function runTest() {
+  let root_element = document.scrollingElement;
+  let target_div = document.getElementById("targetDiv");
+  let inner_div = document.getElementById("innerDiv");
+
+  // Get expected position for root_element scrollIntoView.
+  root_element.scrollTo(10000, 10000);
+  let max_root_x = root_element.scrollLeft;
+  let max_root_y = root_element.scrollTop;
+  root_element.scrollTo(0, 0);
+
+  target_div.scrollTo(10000, 10000);
+  let max_element_x = target_div.scrollLeft;
+  let max_element_y = target_div.scrollTop;
+  target_div.scrollTo(0, 0);
+
+  promise_test (async (t) => {
+    await waitForCompositorCommit();
+    target_div.addEventListener("scrollend", onElementScrollEnd);
+    document.addEventListener("scrollend", onDocumentScrollEnd);
+
+    let test_cases = [
+      [target_div, max_element_x, max_element_y, [inner_div, "scrollIntoView", { inline: "end", block: "end", behavior: "auto" }]],
+      [target_div, 0, 0, [inner_div, "scrollIntoView", { inline: "start", block: "start", behavior: "smooth" }]],
+      [root_element, max_root_x, max_root_y, [root_element, "scrollIntoView", { inline: "end", block: "end", behavior: "smooth" }]],
+      [root_element, 0, 0, [root_element, "scrollIntoView", { inline: "start", block: "start", behavior: "smooth" }]]
+    ];
+
+    for(i = 0; i < test_cases.length; i++) {
+      let t = test_cases[i];
+      let target = t[0];
+      let expected_x = t[1];
+      let expected_y = t[2];
+      let scroll_datas = t[3];
+
+      callScrollFunction(scroll_datas);
+      await waitFor(() => { return element_scrollend_arrived || document_scrollend_arrived; }, target.tagName + ".scrollIntoView  did not receive scrollend event.");
+      if (target == root_element)
+        assert_false(element_scrollend_arrived);
+      else
+        assert_false(document_scrollend_arrived);
+      assert_equals(target.scrollLeft, expected_x, target.tagName + ".scrollIntoView scrollLeft");
+      assert_equals(target.scrollTop, expected_y, target.tagName + ".scrollIntoView scrollTop");
+
+      element_scrollend_arrived = false;
+      document_scrollend_arrived = false;
+    }
+  }, "Tests scrollend event for scrollIntoView.");
+
+  promise_test(async (t) => {
+    document.body.removeChild(target_div);
+    let out_div = document.createElement("div");
+    out_div.style = "width: 100px; height:100px; overflow:scroll; scroll-behavior:smooth;";
+    out_div.appendChild(target_div);
+    document.body.appendChild(out_div);
+    await waitForCompositorCommit();
+
+    element_scrollend_arrived = false;
+    document_scrollend_arrived = false;
+    inner_div.scrollIntoView({ inline: "end", block: "end", behavior: "auto" });
+    await waitFor(() => { return element_scrollend_arrived || document_scrollend_arrived; }, "Nested scrollIntoView did not receive scrollend event.");
+    assert_equals(root_element.scrollLeft, 0, "Nested scrollIntoView root_element scrollLeft");
+    assert_equals(root_element.scrollTop, 0, "Nested scrollIntoView root_element scrollTop");
+    assert_equals(out_div.scrollLeft, 100, "Nested scrollIntoView out_div scrollLeft");
+    assert_equals(out_div.scrollTop, 100, "Nested scrollIntoView out_div scrollTop");
+    assert_equals(target_div.scrollLeft, max_element_x, "Nested scrollIntoView target_div scrollLeft");
+    assert_equals(target_div.scrollTop, max_element_y, "Nested scrollIntoView target_div scrollTop");
+    assert_false(document_scrollend_arrived);
+  }, "Tests scrollend event for nested scrollIntoView.");
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-to-document.html b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-to-document.html
new file mode 100644
index 0000000000..3090455388
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-to-document.html
@@ -0,0 +1,70 @@
+<!DOCTYPE HTML>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+#targetDiv {
+  width: 200px;
+  height: 200px;
+  overflow: scroll;
+}
+
+#innerDiv {
+  width: 400px;
+  height: 400px;
+}
+</style>
+
+<body style="margin:0" onload=runTest()>
+<div id="targetDiv">
+  <div id="innerDiv">
+  </div>
+</div>
+</body>
+
+<script>
+var target_div = document.getElementById('targetDiv');
+var horizontal_scrollend_arrived = false;
+var vertical_scrollend_arrived = false;
+function onHorizontalScrollEnd(event) {
+  assert_false(event.cancelable);
+  // scrollend events are bubbled when the target node is document.
+  assert_true(event.bubbles);
+  horizontal_scrollend_arrived = true;
+}
+function onVerticalScrollEnd(event) {
+  assert_false(event.cancelable);
+  // scrollend events are bubbled when the target node is document.
+  assert_true(event.bubbles);
+  vertical_scrollend_arrived = true;
+}
+
+function runTest() {
+  promise_test (async (t) => {
+    // Make sure that no scrollend event is sent to target_div.
+    target_div.addEventListener("scrollend",
+        t.unreached_func("target_div got unexpected scrollend event."));
+    await waitForCompositorCommit();
+
+    // Scroll left on target div and wait for the doc to get scrollend event.
+    document.addEventListener("scrollend", onHorizontalScrollEnd);
+    await touchScrollInTarget(300, target_div, 'left');
+    await waitFor(() => { return horizontal_scrollend_arrived; },
+        'Document did not receive scrollend event after scroll left on target.');
+    assert_equals(target_div.scrollLeft, 0);
+    document.removeEventListener("scrollend", onHorizontalScrollEnd);
+
+    // Scroll up on target div and wait for the doc to get scrollend event.
+    document.addEventListener("scrollend", onVerticalScrollEnd);
+    await touchScrollInTarget(300, target_div, 'up');
+    await waitFor(() => { return vertical_scrollend_arrived; },
+        'Document did not receive scrollend event after scroll up on target.');
+    assert_equals(target_div.scrollTop, 0);
+  }, 'Tests that the document gets scrollend event when no element scrolls by ' +
+     'touch.');
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-to-element-with-overscroll-behavior.html b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-to-element-with-overscroll-behavior.html
new file mode 100644
index 0000000000..acad168e56
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-to-element-with-overscroll-behavior.html
@@ -0,0 +1,102 @@
+<!DOCTYPE HTML>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+#overscrollXDiv {
+  width: 600px;
+  height: 600px;
+  overflow: scroll;
+  overscroll-behavior-x: contain;
+}
+#overscrollYDiv {
+  width: 500px;
+  height: 500px;
+  overflow: scroll;
+  overscroll-behavior-y: none;
+}
+#targetDiv {
+  width: 400px;
+  height: 400px;
+  overflow: scroll;
+}
+.content {
+  width:800px;
+  height:800px;
+}
+</style>
+
+<body style="margin:0" onload=runTest()>
+<div id="overscrollXDiv">
+  <div class=content>
+    <div id="overscrollYDiv">
+      <div class=content>
+        <div id="targetDiv">
+          <div class="content">
+          </div>
+        </div>
+      </div>
+    </div>
+  </div>
+</div>
+</body>
+
+<script>
+var target_div = document.getElementById('targetDiv');
+var horizontal_scrollend_arrived = false;
+var vertical_scrollend_arrived = false;
+function onHorizontalScrollEnd(event) {
+  assert_false(event.cancelable);
+  assert_false(event.bubbles);
+  horizontal_scrollend_arrived = true;
+}
+function onVerticalScrollEnd(event) {
+  assert_false(event.cancelable);
+  assert_false(event.bubbles);
+  vertical_scrollend_arrived = true;
+}
+// Test that both "onscrollend" and addEventListener("scrollend"... work.
+document.getElementById('overscrollXDiv').onscrollend = onHorizontalScrollEnd;
+document.getElementById('overscrollYDiv').
+    addEventListener("scrollend", onVerticalScrollEnd);
+
+function runTest() {
+  promise_test (async (t) => {
+    // Make sure that no scrollend event is sent to document or target_div.
+    document.addEventListener("scrollend",
+        t.unreached_func("Document got unexpected scrollend event."));
+    target_div.addEventListener("scrollend",
+        t.unreached_func("target_div got unexpected scrollend event."));
+    await waitForCompositorCommit();
+
+    // Scroll left on target div and wait for the element with overscroll-x to
+    // get scrollend event.
+    await touchScrollInTarget(300, target_div, 'left');
+    await waitFor(() => { return horizontal_scrollend_arrived; },
+        'Expected element did not receive scrollend event after scroll left ' +
+        'on target.');
+    assert_equals(target_div.scrollLeft, 0);
+
+    let touchEndPromise = new Promise((resolve) => {
+      target_div.addEventListener("touchend", resolve);
+    });
+    await touchScrollInTarget(300, target_div, 'up');
+
+    // The scrollend event should never be fired before the gesture has completed.
+    await touchEndPromise;
+
+    // Ensure we wait at least a tick after the touch end.
+    await waitForCompositorCommit();
+
+    // We should not trigger a scrollend event for a scroll that did not change
+    // the scroll position.
+    assert_equals(vertical_scrollend_arrived, false);
+    assert_equals(target_div.scrollTop, 0);
+  }, 'Tests that the last element in the cut scroll chain gets scrollend ' +
+     'event when no element scrolls by touch.');
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-to-scrolled-element.html b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-to-scrolled-element.html
new file mode 100644
index 0000000000..7343396942
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-to-scrolled-element.html
@@ -0,0 +1,68 @@
+<!DOCTYPE HTML>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+#scrollableDiv {
+  width: 200px;
+  height: 200px;
+  overflow: scroll;
+}
+
+#innerDiv {
+  width: 400px;
+  height: 400px;
+}
+</style>
+
+<body style="margin:0" onload=runTest()>
+<div id="scrollableDiv">
+  <div id="innerDiv">
+  </div>
+</div>
+</body>
+
+<script>
+var scrolling_div = document.getElementById('scrollableDiv');
+var horizontal_scrollend_arrived = false;
+var vertical_scrollend_arrived = false;
+function onHorizontalScrollEnd(event) {
+  assert_false(event.cancelable);
+  assert_false(event.bubbles);
+  horizontal_scrollend_arrived = true;
+}
+function onVerticalScrollEnd(event) {
+  assert_false(event.cancelable);
+  assert_false(event.bubbles);
+  vertical_scrollend_arrived = true;
+}
+scrolling_div.addEventListener("scrollend", onHorizontalScrollEnd);
+scrolling_div.addEventListener("scrollend", onVerticalScrollEnd);
+
+function runTest() {
+  promise_test (async (t) => {
+    // Make sure that no scrollend event is sent to document.
+    document.addEventListener("scrollend",
+        t.unreached_func("Document got unexpected scrollend event."));
+    await waitForCompositorCommit();
+
+    // Do a horizontal scroll and wait for scrollend event.
+    await touchScrollInTarget(300, scrolling_div, 'right');
+    await waitFor(() => { return horizontal_scrollend_arrived; },
+        'Scroller did not receive scrollend event after horizontal scroll.');
+    assert_equals(scrolling_div.scrollWidth - scrolling_div.scrollLeft,
+                scrolling_div.clientWidth);
+
+    // Do a vertical scroll and wait for scrollend event.
+    await touchScrollInTarget(300, scrolling_div, 'down');
+    await waitFor(() => { return vertical_scrollend_arrived; },
+        'Scroller did not receive scrollend event after vertical scroll.');
+    assert_equals(scrolling_div.scrollHeight - scrolling_div.scrollTop,
+                scrolling_div.clientHeight);
+  }, 'Tests that the scrolled element gets scrollend event at the end of touch scrolling.');
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-to-window.html b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-to-window.html
new file mode 100644
index 0000000000..ef72f56d2b
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-fired-to-window.html
@@ -0,0 +1,55 @@
+<!DOCTYPE HTML>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+#targetDiv {
+  width: 200px;
+  height: 200px;
+  overflow: scroll;
+}
+
+#innerDiv {
+  width: 400px;
+  height: 400px;
+}
+</style>
+
+<body style="margin:0" onload=runTest()>
+<div id="targetDiv">
+  <div id="innerDiv">
+  </div>
+</div>
+</body>
+
+<script>
+var target_div = document.getElementById('targetDiv');
+var scrollend_arrived = false;
+function onScrollEnd(event) {
+  assert_false(event.cancelable);
+  // scrollend events targetting document are bubbled to the window.
+  assert_true(event.bubbles);
+  scrollend_arrived = true;
+}
+window.addEventListener("scrollend", onScrollEnd);
+
+function runTest() {
+  promise_test (async (t) => {
+    // Make sure that no scrollend event is sent to target_div.
+    target_div.addEventListener("scrollend",
+        t.unreached_func("target_div got unexpected scrollend event."));
+    await waitForCompositorCommit();
+
+    // Scroll up on target div and wait for the doc to get scrollend event.
+    await touchScrollInTarget(300, target_div, 'up');
+    await waitFor(() => { return scrollend_arrived; },
+        'Window did not receive scrollend event after scroll up on target.');
+    assert_equals(target_div.scrollTop, 0);
+  }, 'Tests that the window gets scrollend event when no element scrolls ' +
+     'after touch scrolling.');
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/scrolling/scrollend-event-for-user-scroll.html b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-for-user-scroll.html
new file mode 100644
index 0000000000..5146c5f719
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-for-user-scroll.html
@@ -0,0 +1,199 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+    #targetDiv {
+        width: 200px;
+        height: 200px;
+        overflow: scroll;
+    }
+
+    #innerDiv {
+        width: 400px;
+        height: 400px;
+    }
+</style>
+</head>
+<body style="margin:0" onload=runTest()>
+    <div id="targetDiv">
+        <div id="innerDiv">
+        </div>
+    </div>
+</body>
+
+<script>
+var target_div = document.getElementById('targetDiv');
+
+async function resetTargetScrollState(test) {
+  if (target_div.scrollTop != 0 || target_div.scrollLeft != 0) {
+    target_div.scrollTop = 0;
+    target_div.scrollLeft = 0;
+    return waitForScrollendEvent(test, target_div);
+  }
+}
+
+async function verifyScrollStopped(test) {
+  const unscaled_pause_time_in_ms = 100;
+  const x = target_div.scrollLeft;
+  const y = target_div.scrollTop;
+  return new Promise(resolve => {
+    test.step_timeout(() => {
+      assert_equals(x, target_div.scrollLeft);
+      assert_equals(y, target_div.scrollTop);
+      resolve();
+    }, unscaled_pause_time_in_ms);
+  });
+}
+
+async function verifyNoScrollendOnDocument(test) {
+  const callback =
+      test.unreached_func("window got unexpected scrollend event.");
+  window.addEventListener('scrollend', callback);
+}
+
+async function createScrollendPromise(test) {
+  return waitForScrollendEvent(test, target_div).then(evt => {
+      assert_false(evt.cancelable, 'Event is not cancelable');
+      assert_false(evt.bubbles, 'Event targeting element does not bubble');
+  });
+}
+
+function runTest() {
+  promise_test(async (t) => {
+    // Skip the test on a Mac as they do not support touch screens.
+    const isMac = navigator.platform.toUpperCase().indexOf('MAC')>=0;
+    if (isMac)
+      return;
+
+    await resetTargetScrollState(t);
+    await waitForCompositorCommit();
+
+    const targetScrollendPromise = createScrollendPromise(t);
+    verifyNoScrollendOnDocument(t);
+
+    // Perform a touch drag on target div and wait for target_div to get
+    // a scrollend event.
+    await new test_driver.Actions()
+        .addPointer('TestPointer', 'touch')
+        .pointerMove(0, 0, {origin: target_div}) // 0, 0 is center of element.
+        .pointerDown()
+        .addTick()
+        .pointerMove(0, -40, {origin: target_div}) //  Drag up to move down.
+        .addTick()
+        .pause(200) //  Prevent inertial scroll.
+        .pointerUp()
+        .send();
+
+    await targetScrollendPromise;
+
+    assert_true(target_div.scrollTop > 0);
+    await verifyScrollStopped(t);
+  }, 'Tests that the target_div gets scrollend event when touch dragging.');
+
+  promise_test(async (t) => {
+    // Skip test on platforms that do not have a visible scrollbar (e.g.
+    // overlay scrollbar).
+    const scrollbar_width = target_div.offsetWidth - target_div.clientWidth;
+    if (scrollbar_width == 0)
+      return;
+
+    await resetTargetScrollState(t);
+    await waitForCompositorCommit();
+
+    const targetScrollendPromise = createScrollendPromise(t);
+    verifyNoScrollendOnDocument(t);
+
+    const bounds = target_div.getBoundingClientRect();
+    const x = bounds.right - scrollbar_width / 2;
+    const y = bounds.bottom - 20;
+    await new test_driver.Actions()
+        .addPointer('TestPointer', 'mouse')
+        .pointerMove(x, y, {origin: 'viewport'})
+        .pointerDown()
+        .addTick()
+        .pointerUp()
+        .send();
+
+    await targetScrollendPromise;
+    assert_true(target_div.scrollTop > 0);
+    await verifyScrollStopped(t);
+  }, 'Tests that the target_div gets scrollend event when clicking ' +
+     'scrollbar.');
+
+  // Same issue as previous test.
+  promise_test(async (t) => {
+    // Skip test on platforms that do not have a visible scrollbar (e.g.
+    // overlay scrollbar).
+    const scrollbar_width = target_div.offsetWidth - target_div.clientWidth;
+    if (scrollbar_width == 0)
+      return;
+
+    resetTargetScrollState(t);
+    const targetScrollendPromise = createScrollendPromise(t);
+    verifyNoScrollendOnDocument(t);
+
+    const bounds = target_div.getBoundingClientRect();
+    const x = bounds.right - scrollbar_width / 2;
+    const y = bounds.top + 30;
+    const dy = 30;
+    await new test_driver.Actions()
+        .addPointer('TestPointer', 'mouse')
+        .pointerMove(x, y, { origin: 'viewport' })
+        .pointerDown()
+        .pointerMove(x, y + dy, { origin: 'viewport' })
+        .addTick()
+        .pointerUp()
+        .send();
+
+    await targetScrollendPromise;
+    assert_true(target_div.scrollTop > 0);
+    await verifyScrollStopped(t);
+  }, 'Tests that the target_div gets scrollend event when dragging the ' +
+      'scrollbar thumb.');
+
+  promise_test(async (t) => {
+    resetTargetScrollState(t);
+    const targetScrollendPromise = createScrollendPromise(t);
+    verifyNoScrollendOnDocument(t);
+
+    const x = 0;
+    const y = 0;
+    const dx = 0;
+    const dy = 40;
+    const duration_ms = 10;
+    await new test_driver.Actions()
+        .scroll(x, y, dx, dy, { origin: target_div }, duration_ms)
+        .send();
+
+    await targetScrollendPromise;
+    assert_true(target_div.scrollTop > 0);
+    await verifyScrollStopped(t);
+  }, 'Tests that the target_div gets scrollend event when mouse wheel ' +
+     'scrolling.');
+
+  promise_test(async (t) => {
+    await resetTargetScrollState(t);
+    await waitForCompositorCommit();
+
+    verifyNoScrollendOnDocument(t);
+    const targetScrollendPromise = createScrollendPromise(t);
+
+    target_div.focus();
+    window.test_driver.send_keys(target_div, '\ue015');
+
+    await targetScrollendPromise;
+    assert_true(target_div.scrollTop > 0);
+    await verifyScrollStopped(t);
+  }, 'Tests that the target_div gets scrollend event when sending DOWN key ' +
+     'to the target.');
+}
+
+</script>
+</html>
diff --git a/testing/web-platform/tests/dom/events/scrolling/scrollend-event-handler-content-attributes.html b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-handler-content-attributes.html
new file mode 100644
index 0000000000..47f563c39b
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-handler-content-attributes.html
@@ -0,0 +1,108 @@
+<!DOCTYPE HTML>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+html, body {
+  margin: 0
+}
+
+body {
+  height: 3000px;
+  width: 3000px;
+}
+
+#targetDiv {
+  width: 200px;
+  height: 200px;
+  overflow: scroll;
+}
+
+#innerDiv {
+  width: 400px;
+  height: 400px;
+}
+</style>
+
+<body onload=runTest() onscrollend="failOnScrollEnd(event)">
+<div id="targetDiv" onscrollend="onElementScrollEnd(event)">
+  <div id="innerDiv">
+  </div>
+</div>
+</body>
+<script>
+let element_scrollend_arrived = false;
+
+function onElementScrollEnd(event) {
+  assert_false(event.cancelable);
+  assert_false(event.bubbles);
+  element_scrollend_arrived = true;
+}
+
+function failOnScrollEnd(event) {
+  assert_true(false, "Scrollend should not be called on: " + event.target);
+}
+
+function runTest() {
+  let target_div = document.getElementById("targetDiv");
+
+  promise_test (async (t) => {
+    await waitForCompositorCommit();
+
+    target_div.scrollTo({top: 200, left: 200});
+    await waitFor(() => { return element_scrollend_arrived; },
+                  target_div.tagName + " did not receive scrollend event.");
+    assert_equals(target_div.scrollLeft, 200, target_div.tagName + " scrollLeft");
+    assert_equals(target_div.scrollTop, 200, target_div.tagName + " scrollTop");
+  }, "Tests scrollend event is handled by event handler content attribute.");
+
+  promise_test (async (t) => {
+    await waitForCompositorCommit();
+
+    document.scrollingElement.scrollTo({top: 200, left: 200});
+    // The document body onscrollend event handler content attribute will fail
+    // here, if it is fired.
+    await waitForCompositorCommit();
+    assert_equals(document.scrollingElement.scrollLeft, 200,
+                  "Document scrolled on horizontal axis");
+    assert_equals(document.scrollingElement.scrollTop, 200,
+                  "Document scrolled on vertical axis");
+  }, "Tests scrollend event is not fired to document body event handler content attribute.");
+
+  promise_test (async (t) => {
+    await waitForCompositorCommit();
+
+    // Reset the scroll position.
+    document.scrollingElement.scrollTo({top: 0, left: 0});
+
+    let scrollend_event = new Promise(resolve => document.onscrollend = resolve);
+    document.scrollingElement.scrollTo({top: 200, left: 200});
+    await scrollend_event;
+
+    assert_equals(document.scrollingElement.scrollTop, 200,
+                  "Document scrolled on horizontal axis");
+    assert_equals(document.scrollingElement.scrollLeft, 200,
+                  "Document scrolled on vertical axis");
+  }, "Tests scrollend event is fired to document event handler property");
+
+  promise_test (async (t) => {
+    await waitForCompositorCommit();
+
+    // Reset the scroll position.
+    target_div.scrollTo({top: 0, left: 0});
+
+    let scrollend_event = new Promise(resolve => target_div.onscrollend = resolve);
+    target_div.scrollTo({top: 200, left: 200});
+    await scrollend_event;
+
+    assert_equals(target_div.scrollLeft, 200,
+                  target_div.tagName + " scrolled on horizontal axis");
+    assert_equals(target_div.scrollLeft, 200,
+                  target_div.tagName + " scrolled on vertical axis");
+  }, "Tests scrollend event is fired to element event handler property");
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/scrolling/scrollend-event-not-fired-after-removing-scroller.tentative.html b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-not-fired-after-removing-scroller.tentative.html
new file mode 100644
index 0000000000..95447fbd12
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/scrolling/scrollend-event-not-fired-after-removing-scroller.tentative.html
@@ -0,0 +1,84 @@
+<!DOCTYPE HTML>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="scroll_support.js"></script>
+<style>
+#rootDiv {
+  width: 500px;
+  height: 500px;
+}
+
+#targetDiv {
+  width: 200px;
+  height: 200px;
+  overflow: scroll;
+}
+
+#innerDiv {
+  width: 500px;
+  height: 4000px;
+}
+</style>
+
+<body style="margin:0" onload=runTest()>
+</body>
+
+<script>
+let scrollend_arrived = false;
+
+async function setupHtmlAndScrollAndRemoveElement(element_to_remove_id) {
+  document.body.innerHTML=`
+    <div id="rootDiv">
+      <div id="targetDiv">
+        <div id="innerDiv">
+        </div>
+      </div>
+    </div>
+  `;
+  await waitForCompositorCommit();
+
+  const target_div = document.getElementById('targetDiv');
+  const element_to_remove = document.getElementById(element_to_remove_id);
+  let reached_half_scroll = false;
+  scrollend_arrived = false;
+
+  target_div.addEventListener("scrollend", () => {
+    scrollend_arrived = true;
+  });
+
+  target_div.onscroll = () => {
+    // Remove the element after reached half of the scroll offset,
+    if(target_div.scrollTop >= 1000) {
+      reached_half_scroll = true;
+      element_to_remove.remove();
+    }
+  };
+
+  target_div.scrollTo({top:2000, left:0, behavior:"smooth"});
+  await waitFor(() => {return reached_half_scroll; },
+    "target_div never reached scroll offset of 1000");
+  await waitForCompositorCommit();
+}
+
+function runTest() {
+  promise_test (async (t) => {
+    await setupHtmlAndScrollAndRemoveElement("rootDiv");
+    await conditionHolds(() => { return !scrollend_arrived; });
+  }, "No scrollend is received after removing parent div");
+
+  promise_test (async (t) => {
+    await setupHtmlAndScrollAndRemoveElement("targetDiv");
+    await conditionHolds(() => { return !scrollend_arrived; });
+  }, "No scrollend is received after removing scrolling element");
+
+  promise_test (async (t) => {
+    await setupHtmlAndScrollAndRemoveElement("innerDiv");
+    await waitFor(() => { return scrollend_arrived; },
+        'target_div did not receive scrollend event after vertical scroll.');
+  }, "scrollend is received after removing descendant div");
+}
+</script>
diff --git a/testing/web-platform/tests/dom/events/shadow-relatedTarget.html b/testing/web-platform/tests/dom/events/shadow-relatedTarget.html
new file mode 100644
index 0000000000..713555b7d8
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/shadow-relatedTarget.html
@@ -0,0 +1,30 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<!--
+  This test is adopted from Olli Pettay's test case at
+  http://mozilla.pettay.fi/shadow_focus.html
+-->
+<div id="host"></div>
+<input id="lightInput">
+<script>
+const root = host.attachShadow({ mode: "closed" });
+root.innerHTML = "<input id='shadowInput'>";
+
+async_test((test) => {
+  root.getElementById("shadowInput").focus();
+  window.addEventListener("focus", test.step_func_done((e) => {
+    assert_equals(e.relatedTarget, host);
+  }, "relatedTarget should be pointing to shadow host."), true);
+  lightInput.focus();
+}, "relatedTarget should not leak at capturing phase, at window object.");
+
+async_test((test) => {
+  root.getElementById("shadowInput").focus();
+  lightInput.addEventListener("focus", test.step_func_done((e) => {
+    assert_equals(e.relatedTarget, host);
+  }, "relatedTarget should be pointing to shadow host."), true);
+  lightInput.focus();
+}, "relatedTarget should not leak at target.");
+
+</script>
diff --git a/testing/web-platform/tests/dom/events/webkit-animation-end-event.html b/testing/web-platform/tests/dom/events/webkit-animation-end-event.html
new file mode 100644
index 0000000000..4186f6b7a9
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/webkit-animation-end-event.html
@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Prefixed CSS Animation end events</title>
+<link rel="help" href="https://dom.spec.whatwg.org/#concept-event-listener-invoke">
+
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body>
+
+<script src="resources/prefixed-animation-event-tests.js"></script>
+<script>
+'use strict';
+
+runAnimationEventTests({
+  unprefixedType: 'animationend',
+  prefixedType: 'webkitAnimationEnd',
+  animationCssStyle: '1ms',
+});
+</script>
diff --git a/testing/web-platform/tests/dom/events/webkit-animation-iteration-event.html b/testing/web-platform/tests/dom/events/webkit-animation-iteration-event.html
new file mode 100644
index 0000000000..fb251972a3
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/webkit-animation-iteration-event.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Prefixed CSS Animation iteration events</title>
+<link rel="help" href="https://dom.spec.whatwg.org/#concept-event-listener-invoke">
+
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body>
+
+<script src="resources/prefixed-animation-event-tests.js"></script>
+<script>
+'use strict';
+
+runAnimationEventTests({
+  unprefixedType: 'animationiteration',
+  prefixedType: 'webkitAnimationIteration',
+  // Use a long duration to avoid missing the animation due to slow machines,
+  // but set a negative delay so that the iteration boundary happens shortly
+  // after the animation starts.
+  animationCssStyle: '100s -99.9s 2',
+});
+</script>
diff --git a/testing/web-platform/tests/dom/events/webkit-animation-start-event.html b/testing/web-platform/tests/dom/events/webkit-animation-start-event.html
new file mode 100644
index 0000000000..ad1036644a
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/webkit-animation-start-event.html
@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Prefixed CSS Animation start events</title>
+<link rel="help" href="https://dom.spec.whatwg.org/#concept-event-listener-invoke">
+
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body>
+
+<script src="resources/prefixed-animation-event-tests.js"></script>
+<script>
+'use strict';
+
+runAnimationEventTests({
+  unprefixedType: 'animationstart',
+  prefixedType: 'webkitAnimationStart',
+  animationCssStyle: '1ms',
+});
+</script>
diff --git a/testing/web-platform/tests/dom/events/webkit-transition-end-event.html b/testing/web-platform/tests/dom/events/webkit-transition-end-event.html
new file mode 100644
index 0000000000..2741824e30
--- /dev/null
+++ b/testing/web-platform/tests/dom/events/webkit-transition-end-event.html
@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Prefixed CSS Transition End event</title>
+<link rel="help" href="https://dom.spec.whatwg.org/#concept-event-listener-invoke">
+
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body>
+
+<script src="resources/prefixed-animation-event-tests.js"></script>
+<script>
+'use strict';
+
+runAnimationEventTests({
+  isTransition: true,
+  unprefixedType: 'transitionend',
+  prefixedType: 'webkitTransitionEnd',
+  animationCssStyle: '1ms',
+});
+</script>