From 36d22d82aa202bb199967e9512281e9a53db42c9 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Sun, 7 Apr 2024 21:33:14 +0200
Subject: Adding upstream version 115.7.0esr.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 testing/web-platform/tests/portals/META.yml        |   4 +
 testing/web-platform/tests/portals/README.md       |   9 +
 .../tests/portals/about-blank-cannot-host.html     |  18 ++
 .../tests/portals/csp/frame-ancestors.sub.html     |  13 ++
 .../tests/portals/csp/frame-src.sub.html           |  49 ++++++
 .../tests/portals/csp/resources/frame-src.sub.html |   4 +
 .../csp/resources/frame-src.sub.html.sub.headers   |   2 +
 ...-manipulation-inside-portal-with-subframes.html |  42 +++++
 .../history-manipulation-inside-portal.html        |  60 +++++++
 .../portals/history/resources/inner-iframe.html    |  13 ++
 .../portals/history/resources/portal-harness.js    |  30 ++++
 ...rtal-manipulate-history-with-subframes.sub.html |  83 +++++++++
 .../resources/portal-manipulate-history.html       |  66 +++++++
 .../history/resources/run-test-in-portal.js        |  16 ++
 ...alelement-event-handler-content-attributes.html |  27 +++
 .../tests/portals/idlharness.window.js             |  18 ++
 .../portals/no-portal-in-sandboxed-popup.html      |  17 ++
 .../tests/portals/portal-activate-data.html        |  94 ++++++++++
 .../tests/portals/portal-activate-default.html     |  58 +++++++
 .../portals/portal-activate-event-constructor.html |  25 +++
 .../tests/portals/portal-activate-event.html       |  41 +++++
 .../tests/portals/portal-non-http-navigation.html  |  37 ++++
 .../tests/portals/portal-onload-event.html         |  16 ++
 .../portals-activate-empty-browsing-context.html   |  26 +++
 .../portals/portals-activate-inside-iframe.html    |  21 +++
 .../portals/portals-activate-inside-portal.html    |  18 ++
 .../portals/portals-activate-network-error.html    |  18 ++
 .../portals-activate-no-browsing-context.html      |  10 ++
 .../tests/portals/portals-activate-resolution.html |  19 +++
 .../tests/portals/portals-activate-twice.html      |  24 +++
 .../portals/portals-activate-while-unloading.html  |  70 ++++++++
 .../tests/portals/portals-adopt-predecessor.html   |  82 +++++++++
 .../web-platform/tests/portals/portals-api.html    |  11 ++
 .../tests/portals/portals-close-window.html        |  20 +++
 .../portals/portals-cross-origin-load.sub.html     |  16 ++
 .../tests/portals/portals-focus.sub.html           | 184 ++++++++++++++++++++
 .../tests/portals/portals-host-exposure.sub.html   |  40 +++++
 .../portals-host-hidden-after-activation.html      |  30 ++++
 .../tests/portals/portals-host-null.html           |  10 ++
 .../portals/portals-host-post-message.sub.html     | 138 +++++++++++++++
 .../portals/portals-navigate-after-adoption.html   |  41 +++++
 .../web-platform/tests/portals/portals-nested.html |  17 ++
 .../tests/portals/portals-no-frame-crash.html      |  30 ++++
 .../tests/portals/portals-post-message.sub.html    | 189 +++++++++++++++++++++
 .../portals/portals-referrer-inherit-header.html   |  23 +++
 .../portals-referrer-inherit-header.html.headers   |   1 +
 .../portals/portals-referrer-inherit-meta.html     |  24 +++
 .../tests/portals/portals-referrer.html            |  61 +++++++
 .../tests/portals/portals-rendering.html           |  22 +++
 .../tests/portals/portals-repeated-activate.html   |  11 ++
 .../portals/portals-set-src-after-activate.html    |  38 +++++
 .../tests/portals/predecessor-fires-unload.html    |  40 +++++
 .../portals/references/portals-rendering.html      |   5 +
 .../portals/resources/attempt-portal-load.html     |  11 ++
 .../tests/portals/resources/blank-host.html        |   8 +
 .../tests/portals/resources/eval-portal.html       |  10 ++
 .../resources/focus-page-with-autofocus.html       |  23 +++
 .../portals/resources/focus-page-with-button.html  |  35 ++++
 .../focus-page-with-x-origin-iframe.sub.html       |  28 +++
 .../tests/portals/resources/invalid.asis           |   1 +
 .../tests/portals/resources/open-blank-host.js     |  14 ++
 .../portal-activate-broadcastchannel.html          |   8 +
 .../resources/portal-activate-data-portal.html     |   9 +
 .../resources/portal-activate-event-portal.html    |  21 +++
 .../resources/portal-activate-in-handler.html      |  51 ++++++
 .../resources/portal-activate-inside-portal.html   |  11 ++
 .../resources/portal-activate-twice-window-1.html  |  12 ++
 .../resources/portal-activate-twice-window-2.html  |  22 +++
 .../portals/resources/portal-close-window.html     |   7 +
 .../resources/portal-embed-and-activate.html       |  15 ++
 .../portal-host-cross-origin-navigate.sub.html     |   7 +
 ...portal-host-hidden-after-activation-portal.html |  14 ++
 .../portal-host-post-message-after-activate.html   |  19 +++
 .../portal-host-post-message-navigate-1.html       |   5 +
 .../portal-host-post-message-navigate-2.html       |   4 +
 .../portal-host-post-message-x-origin.html         |   4 +
 .../resources/portal-host-post-message.html        |  51 ++++++
 .../tests/portals/resources/portal-host.html       |  11 ++
 .../portals/resources/portal-inside-iframe.html    |   4 +
 .../portal-post-message-after-activate-window.html |  23 +++
 ...portal-post-message-before-activate-portal.html |  24 +++
 ...portal-post-message-before-activate-window.html |  13 ++
 ...portal-post-message-during-activate-window.html |  21 +++
 .../resources/portal-post-message-portal.html      |  29 ++++
 .../portal-post-message-x-origin-portal.html       |  11 ++
 .../resources/portal-repeated-activate-window.html |  20 +++
 .../portals-adopt-predecessor-portal.html          |  77 +++++++++
 .../resources/portals-adopt-predecessor.html       |  20 +++
 .../portals/resources/portals-nested-portal.html   |   9 +
 .../resources/portals-rendering-portal.html        |   8 +
 .../resources/postmessage-referrer.sub.html        |   8 +
 .../predecessor-fires-unload-watch-unload.html     |  25 +++
 ...le-portal-adopts-and-activates-predecessor.html |   6 +
 .../simple-portal-adopts-predecessor.html          |   7 +
 .../tests/portals/resources/simple-portal.html     |   6 +
 .../tests/portals/resources/stash-utils.sub.js     |  43 +++++
 .../tests/portals/xfo/portals-xfo-deny.sub.html    |  43 +++++
 .../tests/portals/xfo/portals-xfo-sameorigin.html  |  18 ++
 .../tests/portals/xfo/resources/xfo-deny.asis      |   8 +
 .../portals/xfo/resources/xfo-sameorigin.asis      |   8 +
 100 files changed, 2813 insertions(+)
 create mode 100644 testing/web-platform/tests/portals/META.yml
 create mode 100644 testing/web-platform/tests/portals/README.md
 create mode 100644 testing/web-platform/tests/portals/about-blank-cannot-host.html
 create mode 100644 testing/web-platform/tests/portals/csp/frame-ancestors.sub.html
 create mode 100644 testing/web-platform/tests/portals/csp/frame-src.sub.html
 create mode 100644 testing/web-platform/tests/portals/csp/resources/frame-src.sub.html
 create mode 100644 testing/web-platform/tests/portals/csp/resources/frame-src.sub.html.sub.headers
 create mode 100644 testing/web-platform/tests/portals/history/history-manipulation-inside-portal-with-subframes.html
 create mode 100644 testing/web-platform/tests/portals/history/history-manipulation-inside-portal.html
 create mode 100644 testing/web-platform/tests/portals/history/resources/inner-iframe.html
 create mode 100644 testing/web-platform/tests/portals/history/resources/portal-harness.js
 create mode 100644 testing/web-platform/tests/portals/history/resources/portal-manipulate-history-with-subframes.sub.html
 create mode 100644 testing/web-platform/tests/portals/history/resources/portal-manipulate-history.html
 create mode 100644 testing/web-platform/tests/portals/history/resources/run-test-in-portal.js
 create mode 100644 testing/web-platform/tests/portals/htmlportalelement-event-handler-content-attributes.html
 create mode 100644 testing/web-platform/tests/portals/idlharness.window.js
 create mode 100644 testing/web-platform/tests/portals/no-portal-in-sandboxed-popup.html
 create mode 100644 testing/web-platform/tests/portals/portal-activate-data.html
 create mode 100644 testing/web-platform/tests/portals/portal-activate-default.html
 create mode 100644 testing/web-platform/tests/portals/portal-activate-event-constructor.html
 create mode 100644 testing/web-platform/tests/portals/portal-activate-event.html
 create mode 100644 testing/web-platform/tests/portals/portal-non-http-navigation.html
 create mode 100644 testing/web-platform/tests/portals/portal-onload-event.html
 create mode 100644 testing/web-platform/tests/portals/portals-activate-empty-browsing-context.html
 create mode 100644 testing/web-platform/tests/portals/portals-activate-inside-iframe.html
 create mode 100644 testing/web-platform/tests/portals/portals-activate-inside-portal.html
 create mode 100644 testing/web-platform/tests/portals/portals-activate-network-error.html
 create mode 100644 testing/web-platform/tests/portals/portals-activate-no-browsing-context.html
 create mode 100644 testing/web-platform/tests/portals/portals-activate-resolution.html
 create mode 100644 testing/web-platform/tests/portals/portals-activate-twice.html
 create mode 100644 testing/web-platform/tests/portals/portals-activate-while-unloading.html
 create mode 100644 testing/web-platform/tests/portals/portals-adopt-predecessor.html
 create mode 100644 testing/web-platform/tests/portals/portals-api.html
 create mode 100644 testing/web-platform/tests/portals/portals-close-window.html
 create mode 100644 testing/web-platform/tests/portals/portals-cross-origin-load.sub.html
 create mode 100644 testing/web-platform/tests/portals/portals-focus.sub.html
 create mode 100644 testing/web-platform/tests/portals/portals-host-exposure.sub.html
 create mode 100644 testing/web-platform/tests/portals/portals-host-hidden-after-activation.html
 create mode 100644 testing/web-platform/tests/portals/portals-host-null.html
 create mode 100644 testing/web-platform/tests/portals/portals-host-post-message.sub.html
 create mode 100644 testing/web-platform/tests/portals/portals-navigate-after-adoption.html
 create mode 100644 testing/web-platform/tests/portals/portals-nested.html
 create mode 100644 testing/web-platform/tests/portals/portals-no-frame-crash.html
 create mode 100644 testing/web-platform/tests/portals/portals-post-message.sub.html
 create mode 100644 testing/web-platform/tests/portals/portals-referrer-inherit-header.html
 create mode 100644 testing/web-platform/tests/portals/portals-referrer-inherit-header.html.headers
 create mode 100644 testing/web-platform/tests/portals/portals-referrer-inherit-meta.html
 create mode 100644 testing/web-platform/tests/portals/portals-referrer.html
 create mode 100644 testing/web-platform/tests/portals/portals-rendering.html
 create mode 100644 testing/web-platform/tests/portals/portals-repeated-activate.html
 create mode 100644 testing/web-platform/tests/portals/portals-set-src-after-activate.html
 create mode 100644 testing/web-platform/tests/portals/predecessor-fires-unload.html
 create mode 100644 testing/web-platform/tests/portals/references/portals-rendering.html
 create mode 100644 testing/web-platform/tests/portals/resources/attempt-portal-load.html
 create mode 100644 testing/web-platform/tests/portals/resources/blank-host.html
 create mode 100644 testing/web-platform/tests/portals/resources/eval-portal.html
 create mode 100644 testing/web-platform/tests/portals/resources/focus-page-with-autofocus.html
 create mode 100644 testing/web-platform/tests/portals/resources/focus-page-with-button.html
 create mode 100644 testing/web-platform/tests/portals/resources/focus-page-with-x-origin-iframe.sub.html
 create mode 100644 testing/web-platform/tests/portals/resources/invalid.asis
 create mode 100644 testing/web-platform/tests/portals/resources/open-blank-host.js
 create mode 100644 testing/web-platform/tests/portals/resources/portal-activate-broadcastchannel.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-activate-data-portal.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-activate-event-portal.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-activate-in-handler.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-activate-inside-portal.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-activate-twice-window-1.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-activate-twice-window-2.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-close-window.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-embed-and-activate.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-host-cross-origin-navigate.sub.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-host-hidden-after-activation-portal.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-host-post-message-after-activate.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-host-post-message-navigate-1.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-host-post-message-navigate-2.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-host-post-message-x-origin.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-host-post-message.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-host.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-inside-iframe.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-post-message-after-activate-window.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-post-message-before-activate-portal.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-post-message-before-activate-window.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-post-message-during-activate-window.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-post-message-portal.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-post-message-x-origin-portal.html
 create mode 100644 testing/web-platform/tests/portals/resources/portal-repeated-activate-window.html
 create mode 100644 testing/web-platform/tests/portals/resources/portals-adopt-predecessor-portal.html
 create mode 100644 testing/web-platform/tests/portals/resources/portals-adopt-predecessor.html
 create mode 100644 testing/web-platform/tests/portals/resources/portals-nested-portal.html
 create mode 100644 testing/web-platform/tests/portals/resources/portals-rendering-portal.html
 create mode 100644 testing/web-platform/tests/portals/resources/postmessage-referrer.sub.html
 create mode 100644 testing/web-platform/tests/portals/resources/predecessor-fires-unload-watch-unload.html
 create mode 100644 testing/web-platform/tests/portals/resources/simple-portal-adopts-and-activates-predecessor.html
 create mode 100644 testing/web-platform/tests/portals/resources/simple-portal-adopts-predecessor.html
 create mode 100644 testing/web-platform/tests/portals/resources/simple-portal.html
 create mode 100644 testing/web-platform/tests/portals/resources/stash-utils.sub.js
 create mode 100644 testing/web-platform/tests/portals/xfo/portals-xfo-deny.sub.html
 create mode 100644 testing/web-platform/tests/portals/xfo/portals-xfo-sameorigin.html
 create mode 100644 testing/web-platform/tests/portals/xfo/resources/xfo-deny.asis
 create mode 100644 testing/web-platform/tests/portals/xfo/resources/xfo-sameorigin.asis

(limited to 'testing/web-platform/tests/portals')

diff --git a/testing/web-platform/tests/portals/META.yml b/testing/web-platform/tests/portals/META.yml
new file mode 100644
index 0000000000..2b3241dd18
--- /dev/null
+++ b/testing/web-platform/tests/portals/META.yml
@@ -0,0 +1,4 @@
+spec: https://wicg.github.io/portals/
+suggested_reviewers:
+  - jeremyroman
+  - lucasgadani
diff --git a/testing/web-platform/tests/portals/README.md b/testing/web-platform/tests/portals/README.md
new file mode 100644
index 0000000000..29134d490f
--- /dev/null
+++ b/testing/web-platform/tests/portals/README.md
@@ -0,0 +1,9 @@
+# Portals
+
+This directory contains tests for the portals feature, which seeks to enable
+seamless navigation. For more information, see:
+
+* https://github.com/WICG/portals
+* https://wicg.github.io/portals/
+
+This feature is currently in early development.
diff --git a/testing/web-platform/tests/portals/about-blank-cannot-host.html b/testing/web-platform/tests/portals/about-blank-cannot-host.html
new file mode 100644
index 0000000000..c43fbc93ba
--- /dev/null
+++ b/testing/web-platform/tests/portals/about-blank-cannot-host.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+
+promise_test(async (t) => {
+  assert_implements("HTMLPortalElement" in self);
+  let hostWindow = window.open();
+  assert_equals(hostWindow.location.href, "about:blank");
+
+  let portal = hostWindow.document.createElement("portal");
+  portal.src = "resources/simple-portal.html";
+  hostWindow.document.body.appendChild(portal);
+
+  await promise_rejects_dom(t, "InvalidStateError", hostWindow.DOMException, portal.activate());
+}, "about:blank cannot host a portal");
+
+</script>
diff --git a/testing/web-platform/tests/portals/csp/frame-ancestors.sub.html b/testing/web-platform/tests/portals/csp/frame-ancestors.sub.html
new file mode 100644
index 0000000000..096ed00c7a
--- /dev/null
+++ b/testing/web-platform/tests/portals/csp/frame-ancestors.sub.html
@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html>
+<meta name="timeout" content="long">
+<head>
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+  <title>Blocked portals are reported correctly</title>
+</head>
+<body>
+  <portal src="/content-security-policy/frame-ancestors/support/content-security-policy.sub.html?policy=report-uri%20/reporting/resources/report.py%3Fop=put%26reportID={{$id:uuid()}}%3B%20frame-ancestors%20'none'"></portal>
+  <script async defer src="/content-security-policy/support/checkReport.sub.js?reportField=violated-directive&reportValue=frame-ancestors%20'none'&reportID={{$id}}"></script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/portals/csp/frame-src.sub.html b/testing/web-platform/tests/portals/csp/frame-src.sub.html
new file mode 100644
index 0000000000..13d9e79667
--- /dev/null
+++ b/testing/web-platform/tests/portals/csp/frame-src.sub.html
@@ -0,0 +1,49 @@
+<!doctype html>
+<title>Tests that portals respect the frame-src</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+</body>
+<script>
+  async_test(function(t) {
+    assert_implements("HTMLPortalElement" in self);
+    var w = window.open("resources/frame-src.sub.html?frame_src_policy=%27none%27");
+    w.onload = function() {
+      w.document.addEventListener("securitypolicyviolation",
+        t.step_func_done(function(e) {
+          assert_equals("frame-src", e.violatedDirective);
+      }));
+      var portal = w.document.createElement("portal");
+      portal.src = new URL("/portals/resources/simple-portal.html", location.href);
+      portal.onmessage = t.unreached_func("Portal should not load.");
+      w.document.body.appendChild(portal);
+    }
+  }, "Tests that a portal can't be loaded when it violates frame-src");
+
+  async_test(function(t) {
+    assert_implements("HTMLPortalElement" in self);
+    var w = window.open(`resources/frame-src.sub.html?frame_src_policy=http://{{hosts[][www]}}:{{ports[http][0]}}`);
+    w.onload = function() {
+      w.document.onsecuritypolicyviolation = t.unreached_func("Portal should load.");
+      var portal = w.document.createElement("portal");
+      portal.src = new URL("http://{{hosts[][www]}}:{{ports[http][0]}}/portals/resources/simple-portal.html", location.href);
+      portal.onmessage = t.step_func_done();
+      w.document.body.appendChild(portal);
+    }
+  }, "Tests that a portal can be loaded when the origin matches the frame-src CSP header.");
+  async_test(function(t) {
+    assert_implements("HTMLPortalElement" in self);
+    var w = window.open(`resources/frame-src.sub.html?frame_src_policy=http://{{hosts[][www]}}:{{ports[http][0]}}`);
+    w.onload = function() {
+      var portal = w.document.createElement("portal");
+      portal.src = new URL("http://{{hosts[alt][www]}}:{{ports[http][0]}}/portals/resources/simple-portal.html", location.href);
+      w.document.onsecuritypolicyviolation = t.step_func(function(e) {
+        w.document.onsecuritypolicyviolation = null;
+        assert_equals("frame-src", e.violatedDirective);
+        portal.src = new URL("http://{{hosts[][www]}}:{{ports[http][0]}}/portals/resources/simple-portal.html", location.href);
+        portal.onmessage = t.step_func_done();
+      });
+      w.document.body.appendChild(portal);
+    }
+  }, "Tests that a portal will fail to load on an origin different than the one specified in the frame-src CSP, but that it can be loaded when the origin matches the frame-src CSP.");
+</script>
diff --git a/testing/web-platform/tests/portals/csp/resources/frame-src.sub.html b/testing/web-platform/tests/portals/csp/resources/frame-src.sub.html
new file mode 100644
index 0000000000..c4f742a643
--- /dev/null
+++ b/testing/web-platform/tests/portals/csp/resources/frame-src.sub.html
@@ -0,0 +1,4 @@
+<!doctype html>
+<body>
+  <h1>Content Security Policy header containing "frame-src {{GET[frame_src_policy]}}"</h1>
+</body>
diff --git a/testing/web-platform/tests/portals/csp/resources/frame-src.sub.html.sub.headers b/testing/web-platform/tests/portals/csp/resources/frame-src.sub.html.sub.headers
new file mode 100644
index 0000000000..d50520cd39
--- /dev/null
+++ b/testing/web-platform/tests/portals/csp/resources/frame-src.sub.html.sub.headers
@@ -0,0 +1,2 @@
+Content-Type: text/html; charset=UTF-8
+Content-Security-Policy: frame-src {{GET[frame_src_policy]}}
diff --git a/testing/web-platform/tests/portals/history/history-manipulation-inside-portal-with-subframes.html b/testing/web-platform/tests/portals/history/history-manipulation-inside-portal-with-subframes.html
new file mode 100644
index 0000000000..cb4c8d0f91
--- /dev/null
+++ b/testing/web-platform/tests/portals/history/history-manipulation-inside-portal-with-subframes.html
@@ -0,0 +1,42 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/run-test-in-portal.js"></script>
+<body>
+<script>
+  var portalSrc =
+      'resources/portal-manipulate-history-with-subframes.sub.html';
+
+  // Runs before and after the history manipulation in the portal to confirm
+  // that the session history of the portal host is not affected by any history
+  // changes in the portal.
+  function assertInitialHistoryState() {
+    assert_equals(history.length, 1);
+    assert_false(!!history.state);
+  }
+
+  promise_test(async () => {
+    assertInitialHistoryState();
+    await runTestInPortal(portalSrc, 'testIFrameSrcInPortal');
+    assertInitialHistoryState();
+  }, 'Setting iframe src navigates independently with replacement in a portal');
+
+  promise_test(async () => {
+    assertInitialHistoryState();
+    await runTestInPortal(portalSrc, 'testCrossSiteIFrameSrcInPortal');
+    assertInitialHistoryState();
+  }, 'Setting cross site iframe src navigates independently with replacement in a portal');
+
+  promise_test(async () => {
+    assertInitialHistoryState();
+    await runTestInPortal(portalSrc, 'testIFrameNavInPortal');
+    assertInitialHistoryState();
+  }, 'iframe navigates itself independently with replacement in a portal');
+
+  promise_test(async () => {
+    assertInitialHistoryState();
+    await runTestInPortal(portalSrc, 'testCrossSiteIFrameNavInPortal');
+    assertInitialHistoryState();
+  }, 'Cross site iframe navigates itself independently with replacement in a portal');
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/history/history-manipulation-inside-portal.html b/testing/web-platform/tests/portals/history/history-manipulation-inside-portal.html
new file mode 100644
index 0000000000..d4b0cf4db9
--- /dev/null
+++ b/testing/web-platform/tests/portals/history/history-manipulation-inside-portal.html
@@ -0,0 +1,60 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/run-test-in-portal.js"></script>
+<body>
+<script>
+  var portalSrc =
+      'resources/portal-manipulate-history.html';
+
+  // Runs before and after the history manipulation in the portal to confirm
+  // that the session history of the portal host is not affected by any history
+  // changes in the portal.
+  function assertInitialHistoryState() {
+    assert_equals(history.length, 1);
+    assert_false(!!history.state);
+  }
+
+  promise_test(async () => {
+    assert_implements("HTMLPortalElement" in self);
+    assertInitialHistoryState();
+    await runTestInPortal(portalSrc, 'testHistoryPushStateInPortal');
+    assertInitialHistoryState();
+  }, 'history.pushState navigates independently with replacement in a portal');
+
+  promise_test(async () => {
+    assert_implements("HTMLPortalElement" in self);
+    assertInitialHistoryState();
+    await runTestInPortal(portalSrc, 'testHistoryReplaceStateInPortal');
+    assertInitialHistoryState();
+  }, 'history.replaceState navigates independently in a portal');
+
+  promise_test(async () => {
+    assert_implements("HTMLPortalElement" in self);
+    assertInitialHistoryState();
+    await runTestInPortal(portalSrc, 'testLocationAssignInPortal');
+    assertInitialHistoryState();
+  }, 'location.assign navigates independently with replacement in a portal');
+
+  promise_test(async () => {
+    assert_implements("HTMLPortalElement" in self);
+    assertInitialHistoryState();
+    await runTestInPortal(portalSrc, 'testLocationReplaceInPortal');
+    assertInitialHistoryState();
+  }, 'location.replace navigates independently in a portal');
+
+  promise_test(async () => {
+    assert_implements("HTMLPortalElement" in self);
+    assertInitialHistoryState();
+    await runTestInPortal(portalSrc, 'testSetLocationHrefInPortal');
+    assertInitialHistoryState();
+  }, 'Setting location.href navigates independently with replacement in a portal');
+
+  promise_test(async () => {
+    assert_implements("HTMLPortalElement" in self);
+    assertInitialHistoryState();
+    await runTestInPortal(portalSrc, 'testSyntheticAnchorClickInPortal');
+    assertInitialHistoryState();
+  }, 'Synthetic anchor click navigates independently with replacement in a portal');
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/history/resources/inner-iframe.html b/testing/web-platform/tests/portals/history/resources/inner-iframe.html
new file mode 100644
index 0000000000..5c6daa22a5
--- /dev/null
+++ b/testing/web-platform/tests/portals/history/resources/inner-iframe.html
@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    window.onmessage = (e) => {
+      if (e.data == 'reportHistoryLength') {
+        e.source.postMessage(history.length, '*');
+      } else if (e.data == 'navigate') {
+        location.href = '#test';
+        e.source.postMessage('Done', '*');
+      }
+    };
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/history/resources/portal-harness.js b/testing/web-platform/tests/portals/history/resources/portal-harness.js
new file mode 100644
index 0000000000..fa8c761afb
--- /dev/null
+++ b/testing/web-platform/tests/portals/history/resources/portal-harness.js
@@ -0,0 +1,30 @@
+// We don't have the test harness in this context, so we roll our own
+// which communicates with our host which is actually running the tests.
+
+window.onload = async () => {
+  let urlParams = new URLSearchParams(window.location.search);
+  let testName = urlParams.get('testName');
+  let testFn = window[testName];
+  if (!testFn) {
+    window.portalHost.postMessage('Missing test: ' + testName);
+    return;
+  }
+
+  // The document load event is not finished at this point, so navigations
+  // would be done with replacement. This interferes with our tests. We wait
+  // for the next task before navigating to avoid this.
+  await new Promise((resolve) => { window.setTimeout(resolve); });
+
+  try {
+    await testFn();
+    window.portalHost.postMessage('Passed');
+  } catch (e) {
+    window.portalHost.postMessage(
+        'Failed: ' + e.name + ': ' + e.message);
+  }
+};
+
+function assert(condition, message) {
+  if (!condition)
+    throw new Error('Assertion failed: ' + message);
+}
diff --git a/testing/web-platform/tests/portals/history/resources/portal-manipulate-history-with-subframes.sub.html b/testing/web-platform/tests/portals/history/resources/portal-manipulate-history-with-subframes.sub.html
new file mode 100644
index 0000000000..bab83b444f
--- /dev/null
+++ b/testing/web-platform/tests/portals/history/resources/portal-manipulate-history-with-subframes.sub.html
@@ -0,0 +1,83 @@
+<!DOCTYPE html>
+<script src="portal-harness.js"></script>
+<body>
+<script>
+  function messageFrameAndAwaitResponse(frame, message) {
+    return new Promise((resolve) => {
+      window.onmessage = (e) => {
+        resolve(e.data);
+      };
+      frame.contentWindow.postMessage(message, '*');
+    });
+  }
+
+  function innerFrameUrl(crossSite) {
+    return (crossSite ?
+                'https://{{hosts[alt][www]}}:{{ports[https][0]}}' : '') +
+            '/portals/history/resources/inner-iframe.html'
+  }
+
+  async function runTestIFrameSrcInPortal(crossSite) {
+    assert(history.length == 1, 'Initial history length');
+
+    let iframe = document.createElement('iframe');
+    iframe.src = innerFrameUrl(crossSite);
+    await new Promise((resolve) => {
+      iframe.onload = resolve;
+      document.body.appendChild(iframe);
+    });
+
+    let frameHistoryLength =
+        await messageFrameAndAwaitResponse(iframe, 'reportHistoryLength');
+    assert(history.length == 1, 'History length unchanged when iframe added');
+    assert(frameHistoryLength == 1, 'History length in iframe when added');
+
+    iframe.src = iframe.src + '#test';
+
+    frameHistoryLength =
+        await messageFrameAndAwaitResponse(iframe, 'reportHistoryLength');
+    assert(
+        history.length == 1, 'History length unchanged when iframe src set');
+    assert(
+        frameHistoryLength == 1,
+        'History length in iframe unchanged when iframe src set');
+  }
+
+  function testIFrameSrcInPortal() {
+    return runTestIFrameSrcInPortal(false);
+  }
+
+  function testCrossSiteIFrameSrcInPortal() {
+    return runTestIFrameSrcInPortal(true);
+  }
+
+  async function runTestIFrameNavInPortal(crossSite) {
+    assert(history.length == 1, 'Initial history length');
+
+    let iframe = document.createElement('iframe');
+    iframe.src = innerFrameUrl(crossSite);
+    await new Promise((resolve) => {
+      iframe.onload = resolve;
+      document.body.appendChild(iframe);
+    });
+
+    await messageFrameAndAwaitResponse(iframe, 'navigate');
+
+    let frameHistoryLength =
+        await messageFrameAndAwaitResponse(iframe, 'reportHistoryLength');
+    assert(
+        history.length == 1, 'History length unchanged when iframe navigates');
+    assert(
+        frameHistoryLength == 1,
+        'History length in iframe unchanged when iframe navigates');
+  }
+
+  function testIFrameNavInPortal() {
+    return runTestIFrameNavInPortal(false);
+  }
+
+  function testCrossSiteIFrameNavInPortal() {
+    return runTestIFrameNavInPortal(true);
+  }
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/history/resources/portal-manipulate-history.html b/testing/web-platform/tests/portals/history/resources/portal-manipulate-history.html
new file mode 100644
index 0000000000..3e25f0e6f2
--- /dev/null
+++ b/testing/web-platform/tests/portals/history/resources/portal-manipulate-history.html
@@ -0,0 +1,66 @@
+<!DOCTYPE html>
+<script src="portal-harness.js"></script>
+<body>
+<script>
+  function testHistoryPushStateInPortal() {
+    assert(history.length == 1, 'Initial history length');
+    assert(!history.state, 'Initial history state');
+
+    history.pushState('teststate', null, null);
+
+    assert(history.length == 1, 'History length unchanged');
+    assert(history.state == 'teststate', 'Update state');
+  }
+
+  function testHistoryReplaceStateInPortal() {
+    assert(history.length == 1, 'Initial history length');
+    assert(!history.state, 'Initial history state');
+
+    history.replaceState('teststate', null, null);
+
+    assert(history.length == 1, 'History length unchanged');
+    assert(history.state == 'teststate', 'Update state');
+  }
+
+  function testLocationAssignInPortal() {
+    assert(history.length == 1, 'Initial history length');
+    let initialLocation = location.href;
+    location.assign('#test');
+
+    assert(history.length == 1, 'History length unchanged');
+    assert(location.href != initialLocation, 'Update location');
+  }
+
+  function testLocationReplaceInPortal() {
+    assert(history.length == 1, 'Initial history length');
+    let initialLocation = location.href;
+    location.replace('#test');
+
+    assert(history.length == 1, 'History length unchanged');
+    assert(location.href != initialLocation, 'Update location');
+  }
+
+  function testSetLocationHrefInPortal() {
+    assert(history.length == 1, 'Initial history length');
+    let initialLocation = location.href;
+    location.href = '#test';
+
+    assert(history.length == 1, 'History length unchanged');
+    assert(location.href != initialLocation, 'Update location');
+  }
+
+  function testSyntheticAnchorClickInPortal() {
+    assert(history.length == 1, 'Initial history length');
+    let initialLocation = location.href;
+
+    var anchor = document.createElement('a');
+    anchor.href = '#test';
+    document.body.appendChild(anchor);
+
+    anchor.click();
+
+    assert(history.length == 1, 'History length unchanged');
+    assert(location.href != initialLocation, 'Update location');
+  }
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/history/resources/run-test-in-portal.js b/testing/web-platform/tests/portals/history/resources/run-test-in-portal.js
new file mode 100644
index 0000000000..c982a1fac8
--- /dev/null
+++ b/testing/web-platform/tests/portals/history/resources/run-test-in-portal.js
@@ -0,0 +1,16 @@
+// This is called from the portal host which is running with the test harness.
+// This creates a portal and communicates with our ad hoc test harness in the
+// portal context which performs the history manipulation in the portal. We
+// confirm that the history manipulation works as expected in the portal.
+async function runTestInPortal(portalSrc, testName) {
+  let portal = document.createElement('portal');
+  portal.src = portalSrc + '?testName=' + testName;
+  let result = await new Promise((resolve) => {
+    portal.onmessage = (e) => {
+      resolve(e.data);
+    };
+    document.body.appendChild(portal);
+  });
+
+  assert_equals(result, 'Passed');
+}
diff --git a/testing/web-platform/tests/portals/htmlportalelement-event-handler-content-attributes.html b/testing/web-platform/tests/portals/htmlportalelement-event-handler-content-attributes.html
new file mode 100644
index 0000000000..0836c8c00b
--- /dev/null
+++ b/testing/web-platform/tests/portals/htmlportalelement-event-handler-content-attributes.html
@@ -0,0 +1,27 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+// Dispatch of these events is tested elsewhere.
+// This test merely ensures that the event handler content attributes work.
+let eventNames = ["load", "message", "messageerror"];
+test(() => {
+  try {
+    assert_implements("HTMLPortalElement" in self);
+    let portal = document.createElement("portal");
+    for (let eventName of eventNames) {
+      window.testValue = "not fired";
+      portal.setAttribute("on" + eventName, "window.testValue = 'fired'");
+      portal.dispatchEvent(new Event(eventName));
+      assert_equals(window.testValue, "fired", `${eventName} should have fired`);
+
+      window.testValue = "not fired";
+      portal.removeAttribute("on" + eventName);
+      portal.dispatchEvent(new Event(eventName));
+      assert_equals(window.testValue, "not fired", `${eventName} should not have fired`);
+    }
+  } finally {
+    delete window.testValue;
+  }
+}, "Tests that event handler content attributes for supported event names work.");
+</script>
diff --git a/testing/web-platform/tests/portals/idlharness.window.js b/testing/web-platform/tests/portals/idlharness.window.js
new file mode 100644
index 0000000000..b43d17dc56
--- /dev/null
+++ b/testing/web-platform/tests/portals/idlharness.window.js
@@ -0,0 +1,18 @@
+// META: script=/resources/WebIDLParser.js
+// META: script=/resources/idlharness.js
+
+// https://wicg.github.io/portals/
+
+'use strict';
+
+idl_test(
+  ['portals'],
+  ['html', 'dom'],
+  async idl_array => {
+    idl_array.add_objects({
+      HTMLPortalElement: ['document.createElement("portal")'],
+      PortalHost: ['window.portalHost'],
+      PortalActivateEvent: ['new PortalActivateEvent("portalactivate")'],
+    });
+  }
+);
diff --git a/testing/web-platform/tests/portals/no-portal-in-sandboxed-popup.html b/testing/web-platform/tests/portals/no-portal-in-sandboxed-popup.html
new file mode 100644
index 0000000000..b26b836467
--- /dev/null
+++ b/testing/web-platform/tests/portals/no-portal-in-sandboxed-popup.html
@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<body>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+
+promise_test(async t => {
+  let sandboxFlags = 'allow-scripts allow-same-origin';
+  let w = window.open(`resources/attempt-portal-load.html?pipe=header(Content-Security-Policy,sandbox ${sandboxFlags})`);
+  await new Promise((resolve, reject) => w.addEventListener('load', resolve));
+  let result = await Promise.race([
+      w.portalLoaded.then(() => 'loaded'),
+      new Promise(resolve => t.step_timeout(() => resolve('timed out'), 5000))]);
+  assert_equals(result, 'timed out', 'expected portal not to load due to sandbox flags');
+});
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portal-activate-data.html b/testing/web-platform/tests/portals/portal-activate-data.html
new file mode 100644
index 0000000000..54fdca5d8c
--- /dev/null
+++ b/testing/web-platform/tests/portals/portal-activate-data.html
@@ -0,0 +1,94 @@
+<!DOCTYPE html>
+<title>Tests passing of data along with portal activation</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/open-blank-host.js"></script>
+<body>
+<canvas id="canvas"></canvas>
+<script>
+function nextMessage(target) {
+  return new Promise((resolve, reject) => {
+    target.addEventListener('message', e => resolve(e), {once: true});
+  });
+}
+
+async function openPortalAndActivate(logic, activateOptions, testWindow) {
+  assert_implements("HTMLPortalElement" in self);
+  const w = testWindow || await openBlankPortalHost();
+  try {
+    const portal = w.document.createElement('portal');
+    portal.src = new URL('resources/portal-activate-data-portal.html?logic=' + encodeURIComponent(logic), location.href);
+    w.document.body.appendChild(portal);
+    assert_equals((await nextMessage(portal)).data, 'ready');
+    await portal.activate(activateOptions);
+    return (await nextMessage(w.portalHost)).data;
+  } finally {
+    w.close();
+  }
+}
+
+promise_test(async () => {
+  const {echo} = await openPortalAndActivate(
+      'return {echo: event.data}',
+      {data: 'banana'});
+  assert_equals(echo, 'banana');
+}, "A string can be passed through activate data.");
+
+promise_test(async () => {
+  let aBuff = new ArrayBuffer(5);
+  let arr = new Int8Array(aBuff);
+  for (var i = 0; i < 5; i++)
+    arr[i] = i;
+  const {array} = await openPortalAndActivate(
+    'return {array: Array.prototype.slice.call(new Int8Array(event.data))}',
+    {data: aBuff, transfer: [aBuff]});
+  assert_equals(arr.length, 0);
+  assert_array_equals(array, [0, 1, 2, 3, 4]);
+}, "An array buffer can be transferred through activate data.");
+
+promise_test(async () => {
+  let canvas = document.getElementById("canvas");
+  let ctx = canvas.getContext("2d");
+  ctx.fillStyle = "green";
+  ctx.fillRect(0, 0, 150, 100);
+  let imageBitmap = await createImageBitmap(canvas, 0, 0, 150, 100);
+  const {height, width} = await openPortalAndActivate(
+    'return {height: event.data.height, width: event.data.width}',
+    {data: imageBitmap, transfer: [imageBitmap]});
+  assert_equals(height, 100);
+  assert_equals(width, 150);
+}, "An image bitmap can be transferred through activate data.");
+
+promise_test(async () => {
+  let {port1, port2} = new MessageChannel();
+  let replyViaPort = nextMessage(port1);
+  port1.start();
+  let ok = await openPortalAndActivate(
+      'let port2 = event.data; port2.postMessage(42); return true;',
+      {data: port2, transfer: [port2]});
+  assert_true(ok);
+  assert_equals((await replyViaPort).data, 42);
+}, "A message port can be passed through activate data.");
+
+promise_test(async t => {
+  const w = await openBlankPortalHost();
+  await promise_rejects_dom(
+      t, 'DataCloneError', w.DOMException,
+      // See https://github.com/whatwg/html/issues/5380 for why not `new SharedArrayBuffer()`
+      openPortalAndActivate('', {data: new WebAssembly.Memory({ shared:true, initial:1, maximum:1 }).buffer}, w));
+}, "A SharedArrayBuffer cannot be passed through activate data.");
+
+promise_test(async t => {
+  await promise_rejects_js(
+      t, Error,
+      openPortalAndActivate('', {data: {get a() { throw new Error; }}}));
+}, "Uncloneable data has its exception propagated.");
+
+promise_test(async t => {
+  const w = await openBlankPortalHost();
+  await promise_rejects_js(
+      t, w.TypeError,
+      openPortalAndActivate('', {data: null, transfer: [null]}, w));
+}, "Errors during transfer list processing are propagated.");
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portal-activate-default.html b/testing/web-platform/tests/portals/portal-activate-default.html
new file mode 100644
index 0000000000..b1a8feb1f4
--- /dev/null
+++ b/testing/web-platform/tests/portals/portal-activate-default.html
@@ -0,0 +1,58 @@
+<!DOCTYPE html>
+<meta name="timeout" content="long">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/open-blank-host.js"></script>
+<script>
+promise_test(async t => {
+  assert_implements("HTMLPortalElement" in self);
+  const w = await openBlankPortalHost();
+  try {
+    const bc = new BroadcastChannel('click-activate');
+    const portal = w.document.createElement('portal');
+    portal.src = new URL(`resources/portal-activate-broadcastchannel.html?bc=${bc.name}`, location.href);
+    w.document.body.appendChild(portal);
+    await new Promise(resolve => portal.onload = resolve);
+    let activated = new Promise(resolve => bc.onmessage = e => resolve(e.data));
+    portal.click();
+    let {event, data} = await activated;
+    assert_equals(event, 'portalactivate');
+    assert_equals(data, undefined);
+  } finally {
+    w.close();
+  }
+}, "Clicking should activate with undefined data.");
+
+promise_test(async t => {
+  assert_implements("HTMLPortalElement" in self);
+  const w = await openBlankPortalHost();
+  try {
+    const bc = new BroadcastChannel('prevent-no-activate');
+    const portal = w.document.createElement('portal');
+    portal.src = new URL(`resources/portal-activate-broadcastchannel.html?bc=${bc.name}`, location.href);
+    portal.onclick = e => e.preventDefault();
+    w.document.body.appendChild(portal);
+    await new Promise(resolve => portal.onload = resolve);
+    bc.onmessage = t.unreached_func('activation should not occur');
+    portal.click();
+    await new Promise(resolve => t.step_timeout(resolve, 3000));
+  } finally {
+    w.close();
+  }
+}, "Clicking shouldn't activate if prevented.");
+
+// Script didn't create the promise so it shouldn't observe one.
+// This forecloses a naive implementation of this behavior that simply calls the WebIDL operation.
+promise_test(async t => {
+  assert_implements("HTMLPortalElement" in self);
+  const w = await openBlankPortalHost();
+  try {
+    const portal = w.document.createElement('portal');
+    w.onunhandledrejection = t.unreached_func('unhandledrejection event should not fire');
+    portal.click();
+    await new Promise(resolve => t.step_timeout(resolve, 3000));
+  } finally {
+    w.close();
+  }
+}, "Failed activation should not surface as an unhandled promise rejection.");
+</script>
diff --git a/testing/web-platform/tests/portals/portal-activate-event-constructor.html b/testing/web-platform/tests/portals/portal-activate-event-constructor.html
new file mode 100644
index 0000000000..1931e8fc86
--- /dev/null
+++ b/testing/web-platform/tests/portals/portal-activate-event-constructor.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+test(() => {
+  // Even though UA-generated portalactivate events are different, the
+  // properties supplied should be used.
+  const e = new PortalActivateEvent("eventtype", { bubbles: true, cancelable: true });
+  assert_equals(e.type, "eventtype");
+  assert_true(e.bubbles);
+  assert_true(e.cancelable);
+  assert_equals(null, e.data);
+}, "It should be possible to construct a PortalActivateEvent with a dictionary");
+
+test(() => {
+  const data = {};
+  const e = new PortalActivateEvent("portalactivate", { data });
+  assert_equals(data, e.data);
+}, "A PortalActivateEvent should expose exactly the data object supplied in the original realm");
+
+test(() => {
+  const e = new PortalActivateEvent("portalactivate");
+  assert_throws_dom("InvalidStateError", () => e.adoptPredecessor());
+}, "Invoking adoptPredecessor on a synthetic PortalActivateEvent should throw");
+</script>
diff --git a/testing/web-platform/tests/portals/portal-activate-event.html b/testing/web-platform/tests/portals/portal-activate-event.html
new file mode 100644
index 0000000000..69d8a7c930
--- /dev/null
+++ b/testing/web-platform/tests/portals/portal-activate-event.html
@@ -0,0 +1,41 @@
+<!DOCTYPE html>
+<title>Tests that the PortalActivateEvent is dispatched when a portal is activated</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+  async_test(function(t) {
+    assert_implements("HTMLPortalElement" in self);
+    let test = "eventlistener";
+    var bc = new BroadcastChannel(`test-${test}`);
+    bc.onmessage = t.step_func_done(function(e) {
+      assert_equals(e.data, "passed");
+      bc.close();
+    });
+    const portalUrl = encodeURIComponent(`portal-activate-event-portal.html?test=${test}`);
+    window.open(`resources/portal-embed-and-activate.html?url=${portalUrl}`);
+  }, "Tests that the PortalActivateEvent is dispatched when a portal is activated.");
+
+  async_test(function(t) {
+    assert_implements("HTMLPortalElement" in self);
+    let test = "eventhandler";
+    var bc = new BroadcastChannel(`test-${test}`);
+    bc.onmessage = t.step_func_done(function(e) {
+      assert_equals(e.data, "passed");
+      bc.close();
+    });
+    const portalUrl = encodeURIComponent(`portal-activate-event-portal.html?test=${test}`);
+    window.open(`resources/portal-embed-and-activate.html?url=${portalUrl}`);
+  }, "Tests that the portalactivate event handler is dispatched when a portal is activated.");
+
+  async_test(function(t) {
+    assert_implements("HTMLPortalElement" in self);
+    let test = "bodyeventhandler";
+    var bc = new BroadcastChannel(`test-${test}`);
+    bc.onmessage = t.step_func_done(function(e) {
+      assert_equals(e.data, "passed");
+      bc.close();
+    });
+    const portalUrl = encodeURIComponent(`portal-activate-event-portal.html?test=${test}`);
+    window.open(`resources/portal-embed-and-activate.html?url=${portalUrl}`);
+  }, "Tests that the HTMLBodyElement has the portalactivate event handler.");
+</script>
diff --git a/testing/web-platform/tests/portals/portal-non-http-navigation.html b/testing/web-platform/tests/portals/portal-non-http-navigation.html
new file mode 100644
index 0000000000..aa02c15efa
--- /dev/null
+++ b/testing/web-platform/tests/portals/portal-non-http-navigation.html
@@ -0,0 +1,37 @@
+<!DOCTYPE html>
+<title>Tests that portal don't navigate to non-http schemes.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<script>
+async_test(t => {
+  assert_implements("HTMLPortalElement" in self);
+  var portal = document.createElement("portal");
+  portal.src = "data:text/html,empty portal";
+  portal.onload = t.unreached_func("Portal loaded data URL.");
+  document.body.appendChild(portal);
+  t.step_timeout(() => { portal.remove(); t.done(); }, 3000);
+}, "Tests that a portal can't navigate to a data URL.");
+
+async_test(t => {
+  assert_implements("HTMLPortalElement" in self);
+  var portal = document.createElement("portal");
+  portal.src = "about:blank";
+  portal.onload = t.unreached_func("Portal loaded about:blank.");
+  document.body.appendChild(portal);
+  t.step_timeout(() => { portal.remove(); t.done(); }, 3000);
+}, "Tests that a portal can't navigate to about:blank.");
+
+async_test(t => {
+  assert_implements("HTMLPortalElement" in self);
+  var portal = document.createElement("portal");
+  portal.src = "resources/simple-portal.html";
+  portal.onload = t.step_func(() => {
+    portal.onmessage = t.unreached_func("Portal execute javascript.");
+    portal.src = "javascript:window.portalHost.postMessage('executed', '*')";
+    t.step_timeout(() => { portal.remove(); t.done(); }, 3000);
+  });
+  document.body.appendChild(portal);
+}, "Tests that a portal can't navigate to javascript URLs.");
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portal-onload-event.html b/testing/web-platform/tests/portals/portal-onload-event.html
new file mode 100644
index 0000000000..f6b97a814e
--- /dev/null
+++ b/testing/web-platform/tests/portals/portal-onload-event.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<title>Tests that the load is dispatched when a portal finishes loading.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+  async_test(function(t) {
+    assert_implements("HTMLPortalElement" in self);
+    var w = window.open("resources/simple-portal.html");
+    w.onload = function() {
+      var portal = w.document.createElement("portal");
+      portal.src = "resources/simple-portal.html";
+      portal.onload = t.step_func_done();
+      w.document.body.appendChild(portal);
+    }
+  }, "Tests that the load event is dispatched when a portal finishes loading.");
+</script>
diff --git a/testing/web-platform/tests/portals/portals-activate-empty-browsing-context.html b/testing/web-platform/tests/portals/portals-activate-empty-browsing-context.html
new file mode 100644
index 0000000000..0c63e38497
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-activate-empty-browsing-context.html
@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<script>
+promise_test(async t => {
+  assert_implements("HTMLPortalElement" in self);
+  let portal = document.createElement('portal');
+  document.body.appendChild(portal);
+  t.add_cleanup(() => { document.body.removeChild(portal); });
+
+  await promise_rejects_dom(t, 'InvalidStateError', portal.activate());
+}, "A portal that has never been navigated cannot be activated");
+
+promise_test(async t => {
+  assert_implements("HTMLPortalElement" in self);
+  let portal = document.createElement('portal');
+  document.body.appendChild(portal);
+  t.add_cleanup(() => { document.body.removeChild(portal); });
+
+  // We use a status of 204 (No Content) as that couldn't possibly mature.
+  portal.src = "/common/blank.html?pipe=status(204)"
+  await promise_rejects_dom(t, 'InvalidStateError', portal.activate());
+}, "A portal that has not completed an initial navigation cannot be activated");
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-activate-inside-iframe.html b/testing/web-platform/tests/portals/portals-activate-inside-iframe.html
new file mode 100644
index 0000000000..f403954096
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-activate-inside-iframe.html
@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+  <script>
+    promise_test(async t => {
+      assert_implements("HTMLPortalElement" in self);
+      var iframe = document.createElement("iframe");
+      iframe.src = "resources/portal-inside-iframe.html"
+      var waitForLoad = new Promise((resolve, reject) => {
+        iframe.onload = resolve;
+      });
+      document.body.appendChild(iframe);
+      await waitForLoad;
+      const portal = iframe.contentDocument.getElementById("portal");
+      return promise_rejects_dom(t, "InvalidStateError",
+                                 iframe.contentWindow.DOMException,
+                                 portal.activate());
+    }, "activating portal inside iframe should fail");
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-activate-inside-portal.html b/testing/web-platform/tests/portals/portals-activate-inside-portal.html
new file mode 100644
index 0000000000..19b57b3e42
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-activate-inside-portal.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+  <script>
+    promise_test(async () => {
+      assert_implements("HTMLPortalElement" in self);
+      var portal = document.createElement("portal");
+      portal.src = "resources/portal-activate-inside-portal.html";
+      let waitForMessage = new Promise((resolve, reject) => {
+        portal.onmessage = e => resolve(e.data);
+        document.body.appendChild(portal);
+      });
+      var error = await waitForMessage;
+      assert_equals(error, "InvalidStateError");
+    }, "activating a nested portal should throw an error");
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-activate-network-error.html b/testing/web-platform/tests/portals/portals-activate-network-error.html
new file mode 100644
index 0000000000..60ee5c902d
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-activate-network-error.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<script>
+async_test(t => {
+  assert_implements("HTMLPortalElement" in self);
+  let portal = document.createElement('portal');
+  portal.src = "resources/invalid.asis";
+  document.body.appendChild(portal);
+  t.add_cleanup(() => { document.body.removeChild(portal); });
+  t.step_timeout(async () => {
+    await promise_rejects_dom(t, 'InvalidStateError', portal.activate());
+    t.done();
+  }, 2000);
+}, "A portal that is showing inline content for a network error cannot be activated");
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-activate-no-browsing-context.html b/testing/web-platform/tests/portals/portals-activate-no-browsing-context.html
new file mode 100644
index 0000000000..ccf1e9504b
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-activate-no-browsing-context.html
@@ -0,0 +1,10 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+promise_test(async t => {
+  assert_implements("HTMLPortalElement" in self);
+  let activatePromise = document.createElement('portal').activate();
+  await promise_rejects_dom(t, 'InvalidStateError', activatePromise);
+}, "A portal with nothing in it cannot be activated");
+</script>
diff --git a/testing/web-platform/tests/portals/portals-activate-resolution.html b/testing/web-platform/tests/portals/portals-activate-resolution.html
new file mode 100644
index 0000000000..7094768a4f
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-activate-resolution.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/open-blank-host.js"></script>
+<script>
+  promise_test(async () => {
+    assert_implements("HTMLPortalElement" in self);
+    var win = await openBlankPortalHost();
+    var portal = win.document.createElement("portal");
+    portal.src = new URL("resources/simple-portal.html", location.href)
+
+    await new Promise((resolve, reject) => {
+      portal.onload = resolve;
+      win.document.body.appendChild(portal);
+    });
+
+    return portal.activate();
+  });
+</script>
diff --git a/testing/web-platform/tests/portals/portals-activate-twice.html b/testing/web-platform/tests/portals/portals-activate-twice.html
new file mode 100644
index 0000000000..0eea5465a2
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-activate-twice.html
@@ -0,0 +1,24 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+promise_test(async t => {
+  assert_implements("HTMLPortalElement" in self);
+  let waitForMessage = new Promise((resolve, reject) => {
+    window.onmessage = e => resolve(e.data);
+  });
+  window.open("resources/portal-activate-twice-window-1.html");
+  let error = await waitForMessage;
+  assert_equals(error, "InvalidStateError");
+}, "Calling activate when a portal is already activating should fail");
+
+promise_test(async t => {
+  assert_implements("HTMLPortalElement" in self);
+  let waitForMessage = new Promise((resolve, reject) => {
+    window.onmessage = e => resolve(e.data);
+  });
+  window.open("resources/portal-activate-twice-window-2.html");
+  let error = await waitForMessage;
+  assert_equals(error, "InvalidStateError");
+});
+</script>
diff --git a/testing/web-platform/tests/portals/portals-activate-while-unloading.html b/testing/web-platform/tests/portals/portals-activate-while-unloading.html
new file mode 100644
index 0000000000..5abb164b3b
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-activate-while-unloading.html
@@ -0,0 +1,70 @@
+<!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-vendor.js"></script>
+    <script>
+      function childReady() {
+        return new Promise((resolve) => {
+          window.onmessage = resolve;
+        });
+      }
+
+      const handlers = ['beforeunload', 'pagehide', 'unload'];
+      for (let handler of handlers) {
+        promise_test(async (test) => {
+          let popup;
+
+          // Open a popup that has a portal, wait for both to be loaded.
+          {
+            await test_driver.bless('Open a popup', () => {
+              popup = open(`resources/portal-activate-in-handler.html?${handler}`,
+                           '_blank');
+            });
+            await childReady();
+          }
+
+          // We need the exception type below to ensure the activate() call
+          // throws but the popup global may be gone by then so stash it here.
+          const exception_type = popup.DOMException;
+
+          // Navigate the popup away.
+          const cur_path = popup.location.pathname;
+          popup.location = 'resources/blank-host.html';
+
+          // We need to wait until the handler is called but because of the
+          // nature of these handlers, we can't reliably communicate with the
+          // popup while they're running so we use a promise established
+          // earlier to wait until a time we know the portal has been activated
+          // and the returned promise stored on this global.
+          await window.handler_called_promise;
+          assert_not_equals(typeof(window.portal_promise), 'undefined',
+                            'Portal.activate() must be called');
+
+          // The popup should have called activate from the handler, and placed
+          // the promise returned from that call into this window in the
+          // |portal_promise| variable. We expect that this call should reject,
+          // however, if it does activate, it's timing dependent whether the
+          // handler will be run to completion so we may never fulfil the
+          // promise. In that case timeout and fail the test.
+          {
+            test.step_timeout(() => {
+              assert_unreached('Activation didn\'t fulfil.');
+            }, 3000);
+
+            await promise_rejects_dom(test,
+                                      "InvalidStateError",
+                                      exception_type,
+                                      window.portal_promise,
+                                      "Portal activation must fail.");
+          }
+          popup.close();
+        }, `cannot activate portal from ${handler}`);
+      }
+    </script>
+  </head>
+  <body>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/portals/portals-adopt-predecessor.html b/testing/web-platform/tests/portals/portals-adopt-predecessor.html
new file mode 100644
index 0000000000..04c6196062
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-adopt-predecessor.html
@@ -0,0 +1,82 @@
+<!DOCTYPE html>
+<title>Tests that a portal can adopt its predecessor</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+  function waitForCompletion(targetTest) {
+    return new Promise((resolve, reject) => {
+      window.addEventListener("message", ({data: {test, message}}) => {
+         if (test === targetTest)
+           resolve(message);
+      });
+    });
+  }
+
+  promise_test(async () => {
+    assert_implements("HTMLPortalElement" in self);
+    var test = "adopt-once";
+    window.open(`resources/portals-adopt-predecessor.html?test=${test}`);
+    var message = await waitForCompletion(test);
+    assert_equals(message, "adopted");
+  }, "Tests that a portal can adopt its predecessor.");
+
+  promise_test(async () => {
+    assert_implements("HTMLPortalElement" in self);
+    var test = "adopt-twice";
+    window.open(`resources/portals-adopt-predecessor.html?test=${test}`);
+    var message = await waitForCompletion(test);
+    assert_equals(message, "passed");
+  }, "Tests that trying to adopt the predecessor twice will throw an exception.");
+
+  async_test(function(t) {
+    assert_implements("HTMLPortalElement" in self);
+    var test = "adopt-after-event";
+    var bc = new BroadcastChannel(`test-${test}`);
+    bc.onmessage = t.step_func_done(function(e) {
+      assert_equals(e.data, "passed");
+      bc.close();
+    });
+    window.open(`resources/portals-adopt-predecessor.html?test=${test}`);
+  }, "Tests that trying to adopt the predecessor after the PortalActivateEvent will throw an exception.");
+
+  promise_test(async t => {
+    assert_implements("HTMLPortalElement" in self);
+    var test = "adopt-and-activate";
+    window.open(`resources/portals-adopt-predecessor.html?test=${test}`);
+    var message = await waitForCompletion(test);
+    assert_equals(message, "passed");
+  }, "Tests that activating an adopted predecessor without inserting it works");
+
+  async_test(t => {
+    assert_implements("HTMLPortalElement" in self);
+    var test = "adopt-attach-remove";
+    var bc = new BroadcastChannel(`test-${test}`);
+    bc.onmessage = t.step_func_done(function(e) {
+      assert_equals(e.data, "passed");
+      bc.close();
+    });
+    window.open(`resources/portals-adopt-predecessor.html?test=${test}`);
+  }, "Tests that an adopting, inserting and then removing a predecessor works correctly");
+
+  async_test(t => {
+    assert_implements("HTMLPortalElement" in self);
+    var test = "adopt-and-discard";
+    var bc = new BroadcastChannel(`test-${test}`);
+    bc.onmessage = t.step_func_done(function(e) {
+      assert_equals(e.data, "passed");
+      bc.close();
+    });
+    window.open(`resources/portals-adopt-predecessor.html?test=${test}`);
+  }, "Tests that the adopted predecessor is destroyed if it isn't inserted");
+
+  async_test(t => {
+    assert_implements("HTMLPortalElement" in self);
+    var test = "adopt-to-disconnected-node";
+    var bc = new BroadcastChannel(`test-${test}`);
+    bc.onmessage = t.step_func_done(function(e) {
+      assert_equals(e.data, "passed");
+      bc.close();
+    });
+    window.open(`resources/portals-adopt-predecessor.html?test=${test}`);
+  }, "Tests that an adopted portal can be inserted into a disconnected node.");
+</script>
diff --git a/testing/web-platform/tests/portals/portals-api.html b/testing/web-platform/tests/portals/portals-api.html
new file mode 100644
index 0000000000..79d2d526bd
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-api.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<title>Portals API test</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+  <script>
+    test(function() {
+      assert_true(document.createElement('portal') instanceof HTMLPortalElement);
+    }, "portal element exists");
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-close-window.html b/testing/web-platform/tests/portals/portals-close-window.html
new file mode 100644
index 0000000000..e3a66c0bf1
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-close-window.html
@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<script>
+promise_test(async t => {
+  assert_implements("HTMLPortalElement" in self);
+  let portal = document.createElement('portal');
+  portal.src = "resources/portal-close-window.html";
+  let waitForMessage = new Promise((resolve, reject) => {
+    portal.onmessage = e => resolve(e.data);
+    document.body.appendChild(portal);
+  });
+  document.body.appendChild(portal);
+  var message = await waitForMessage;
+  assert_equals(message, false);
+  t.add_cleanup(() => { document.body.removeChild(portal); });
+}, "A portal's window cannot be closed");
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-cross-origin-load.sub.html b/testing/web-platform/tests/portals/portals-cross-origin-load.sub.html
new file mode 100644
index 0000000000..04db38a8e9
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-cross-origin-load.sub.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<script>
+  promise_test(async () => {
+    assert_implements("HTMLPortalElement" in self);
+    var portal = document.createElement("portal");
+    portal.src = "http://{{hosts[alt][www]}}:{{ports[http][0]}}/portals/resources/simple-portal.html";
+    return new Promise((resolve, reject) => {
+      portal.onload = resolve;
+      document.body.appendChild(portal);
+    });
+  });
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-focus.sub.html b/testing/web-platform/tests/portals/portals-focus.sub.html
new file mode 100644
index 0000000000..54b4312be0
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-focus.sub.html
@@ -0,0 +1,184 @@
+<!DOCTYPE html>
+<meta name="timeout" content="long">
+<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>
+<script src="resources/open-blank-host.js"></script>
+<body>
+<script>
+  async function createPortal(doc, url) {
+    assert_implements("HTMLPortalElement" in self);
+    let portal = doc.createElement("portal");
+    portal.src = url;
+    doc.body.appendChild(portal);
+    await new Promise(r => portal.onload = r);
+    return portal;
+  }
+
+  promise_test(async t => {
+    let portal = await createPortal(document, new URL("resources/focus-page-with-button.html", location.href));
+    try {
+      portal.onmessage = t.step_func(e => {
+        assert_unreached("button inside portal should not be focused");
+      });
+      portal.postMessage("focus");
+      await new Promise(r => t.step_timeout(r, 500));
+    } finally {
+      document.body.removeChild(portal);
+    }
+  }, "test that an element inside a portal cannot steal focus");
+
+  promise_test(async () => {
+    let portal = await createPortal(document, new URL("resources/focus-page-with-button.html", location.href));
+    try {
+      let activeElementUpdated = new Promise(r => {
+        portal.onmessage = e => r(e.data.activeElementUpdated)
+      });
+      portal.postMessage('focus-update-active-element');
+      assert_true(await activeElementUpdated);
+    } finally {
+      document.body.removeChild(portal);
+    }
+  }, "test that activeElement inside a portal is updated after focus() is called");
+
+  promise_test(async t => {
+    let portal = await createPortal(document, new URL("resources/focus-page-with-x-origin-iframe.sub.html", location.href));
+    try {
+      portal.onmessage = t.step_func(e => {
+        assert_unreached("button inside portal should not be focused");
+      });
+      portal.postMessage("focus");
+      await new Promise(r => t.step_timeout(r, 500));
+    } finally {
+      document.body.removeChild(portal);
+    }
+  }, "test that an element inside a portal's x-origin subframe cannot steal focus");
+
+  promise_test(async () => {
+    let portal = await createPortal(document, new URL("resources/focus-page-with-x-origin-iframe.sub.html", location.href));
+    try {
+      portal.postMessage("focus-update-active-element");
+      let {activeElementUpdated} = await new Promise(r => {
+        portal.onmessage = e => r(e.data);
+      });
+      assert_true(activeElementUpdated);
+    } finally {
+      document.body.removeChild(portal);
+    }
+  }, "test that a portal's x-origin subframe becomes active element on focus");
+
+  promise_test(async t => {
+    let win = await openBlankPortalHost();
+    let doc = win.document;
+    try {
+      let portal = await createPortal(doc, new URL("resources/simple-portal-adopts-predecessor.html", location.href));
+      let button = doc.createElement("button");
+      doc.body.appendChild(button);
+
+      await portal.activate();
+      doc.body.removeChild(portal);
+
+      button.onfocus = t.step_func(() => {
+        assert_unreached("button inside adopted portal should not be focused");
+      });
+      button.focus();
+      await new Promise(r => t.step_timeout(r, 500));
+    } finally {
+      win.close();
+    }
+  }, "test that an element inside an adopted portal cannot steal focus");
+
+  promise_test(async t => {
+    let win = await openBlankPortalHost();
+    let doc = win.document;
+    try {
+      let portal = await createPortal(doc, new URL("resources/simple-portal-adopts-predecessor.html", location.href));
+      let iframe = doc.createElement("iframe");
+      iframe.src = new URL("resources/focus-page-with-button.html",
+                           "http://{{hosts[alt][www]}}:{{ports[http][0]}}/portals/");
+      doc.body.appendChild(iframe);
+      await new Promise(r => iframe.onload = r);
+
+      await portal.activate();
+      doc.body.removeChild(portal);
+
+      iframe.contentWindow.postMessage("focus", "*");
+      window.onmessage = t.step_func(() => {
+        assert_unreached("button inside x-origin iframe inside a portal should not be focused");
+      });
+      await new Promise(r => t.step_timeout(r, 500));
+    } finally {
+      win.close();
+    }
+  }, "test that a x-origin iframe inside an adopted portal cannot steal focus");
+
+  promise_test(async () => {
+    let win = await openBlankPortalHost();
+    let doc = win.document;
+    try {
+      let portal = await createPortal(doc, new URL("resources/focus-page-with-autofocus.html", location.href));
+      portal.postMessage('check-active-element');
+      let result = await new Promise(r => {
+        portal.onmessage = e => r(e.data);
+      });
+      assert_true(result, "autofocused element is active element");
+
+      await portal.activate();
+      win.portalHost.postMessage('check-active-element');
+      result = await new Promise(r => {
+        win.portalHost.onmessage = e => r(e.data)
+      });
+      assert_true(result, "autofocused element is still active element");
+    } finally {
+      win.close();
+    }
+  }, "test that autofocus inside a portal works");
+
+  const TAB = "\ue004"; // https://w3c.github.io/webdriver/#keyboard-actions
+  const SPACE = " "
+  const RETURN = "\r";
+
+  promise_test(async t => {
+    let portal = await createPortal(document, "resources/focus-page-with-button.html");
+    try {
+      await test_driver.send_keys(document.body, TAB);
+      portal.onmessage = t.unreached_func("button inside portal should not be focused");
+      await new Promise(r => t.step_timeout(r, 500));
+    } finally {
+      document.body.removeChild(portal);
+    }
+  }, "test that a portal is keyboard focusable");
+
+  promise_test(async t => {
+    let portal = await createPortal(document, "resources/focus-page-with-button.html");
+    try {
+      let portalFocusPromise = new Promise(r => portal.onfocus = r);
+      portal.onmessage = t.unreached_func("button inside portal should not be focused");
+      await test_driver.send_keys(document.body, TAB);
+      await portalFocusPromise;
+      await test_driver.send_keys(document.body, TAB);
+      await new Promise(r => t.step_timeout(r, 500));
+    } finally {
+      document.body.removeChild(portal);
+    }
+  }, "test that we cannot tab into a portal's contents");
+
+  promise_test(async t => {
+    let portal = await createPortal(document, "resources/simple-portal.html");
+    try {
+      portal.focus();
+      for (let key of [SPACE, RETURN]) {
+        let clickPromise = new Promise((resolve) => {
+          portal.onclick = e => { e.preventDefault(); resolve(); };
+        });
+        await test_driver.send_keys(document.body, key);
+        await clickPromise;
+      }
+    } finally {
+      document.body.removeChild(portal);
+    }
+  }, "test that a portal is keyboard activatable");
+
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-host-exposure.sub.html b/testing/web-platform/tests/portals/portals-host-exposure.sub.html
new file mode 100644
index 0000000000..fd3ac18f69
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-host-exposure.sub.html
@@ -0,0 +1,40 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/stash-utils.sub.js"></script>
+<script src="/common/utils.js"></script>
+<body>
+<script>
+  function openPortal(portalSrc) {
+    assert_implements("HTMLPortalElement" in self);
+    const portal = document.createElement('portal');
+    portal.src = portalSrc;
+    return portal;
+  }
+
+  async function openPortalAndReceiveMessage(portalSrc) {
+    const key = token();
+    const portal = openPortal(`${portalSrc}?key=${key}`);
+    document.body.appendChild(portal);
+    return StashUtils.takeValue(key);
+  }
+
+  promise_test(async () => {
+    const result = await openPortalAndReceiveMessage("resources/portal-host.html");
+    assert_equals(result, "passed");
+  }, "window.portalHost should be exposed in same-origin portal");
+
+  promise_test(async () => {
+    const result = await openPortalAndReceiveMessage(
+        "http://{{hosts[alt][www]}}:{{ports[http][0]}}/portals/resources/portal-host.html");
+    assert_equals(result, "passed");
+  }, "window.portalHost should be exposed in cross-origin portal");
+
+  promise_test(async () => {
+    const result = await openPortalAndReceiveMessage(
+        'resources/portal-host-cross-origin-navigate.sub.html');
+    assert_equals(result, "passed");
+  }, "window.portalHost should be exposed in portal after cross-origin navigation");
+
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-host-hidden-after-activation.html b/testing/web-platform/tests/portals/portals-host-hidden-after-activation.html
new file mode 100644
index 0000000000..9638a6c7c6
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-host-hidden-after-activation.html
@@ -0,0 +1,30 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<script>
+  // Waits for 2 messages from portal, one before activation and one after.
+  function waitForMessages() {
+    return new Promise((resolve, reject) => {
+      var results = [];
+      var bc = new BroadcastChannel("portals-host-hidden-after-activation");
+      bc.onmessage = e => {
+        results.push(e.data.hasHost);
+        if (results.length == 2) {
+          bc.close();
+          resolve(results);
+        }
+      };
+    });
+  }
+
+  promise_test(async () => {
+    assert_implements("HTMLPortalElement" in self);
+    const portalUrl = encodeURIComponent("portal-host-hidden-after-activation-portal.html");
+    window.open(`resources/portal-embed-and-activate.html?url=${portalUrl}`);
+    var results = await waitForMessages();
+    assert_true(results[0], "portalHost exposed before calling activate()");
+    assert_false(results[1], "portalHost hidden after receiving portalactivate event");
+  }, "window.portalHost should be null after portal is activated");
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-host-null.html b/testing/web-platform/tests/portals/portals-host-null.html
new file mode 100644
index 0000000000..e0f1d63743
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-host-null.html
@@ -0,0 +1,10 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<script>
+  test(t => {
+    assert_equals(window.portalHost, null, "window.portalHost should be null");
+  });
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-host-post-message.sub.html b/testing/web-platform/tests/portals/portals-host-post-message.sub.html
new file mode 100644
index 0000000000..d589235ec3
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-host-post-message.sub.html
@@ -0,0 +1,138 @@
+<!DOCTYPE html>
+<title>Test postMessage on PortalHost</title>
+<meta name="timeout" content="long">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+  <script>
+    function createPortal(portalSrc) {
+      var portal = document.createElement("portal");
+      portal.src = portalSrc;
+      return new Promise((resolve, reject) => {
+        portal.onload = () => {
+          resolve(portal);
+        };
+        document.body.appendChild(portal);
+      });
+    }
+
+    async function createPortalAndLoopMessage(portalSrc, params) {
+      assert_implements("HTMLPortalElement" in self);
+      var portal = await createPortal(portalSrc);
+      var waitForResponse = new Promise((resolve, reject) => {
+        portal.addEventListener("message", e => { resolve(e); });
+      });
+      portal.postMessage(params);
+      return waitForResponse;
+    }
+
+    const sameOriginUrl = "resources/portal-host-post-message.html";
+    const crossOriginUrl = "http://{{hosts[alt][www]}}:{{ports[http][0]}}/portals/resources/portal-host-post-message-x-origin.html";
+
+    promise_test(async () => {
+      var {data, origin} = await createPortalAndLoopMessage(sameOriginUrl,
+                                                            ["test"]);
+      assert_equals(data, "test");
+      assert_equals(origin, "http://{{host}}:{{ports[http][0]}}");
+    }, "Message received after postMessage from portal host");
+
+    promise_test(async () => {
+      var message = {
+        prop1: "value1",
+        prop2: 2.5,
+        prop3: [1, 2, "3"],
+        prop4: {
+          prop4_1: "value4_1"
+        }
+      };
+      var {data} = await createPortalAndLoopMessage(sameOriginUrl,
+                                                    [message]);
+      assert_object_equals(data, message);
+    }, "postMessage with object message");
+
+    promise_test(async () => {
+      assert_implements("HTMLPortalElement" in self);
+      function checkPort(port) {
+        return new Promise((resolve, reject) => {
+          var channel = new MessageChannel();
+          channel.port1.onmessage = resolve;
+          port.postMessage("sending port", {transfer: [channel.port2]});
+        });
+      }
+
+      var {ports} = await createPortalAndLoopMessage(sameOriginUrl, {
+        type: "message-port"
+      });
+      await checkPort(ports[0]);
+    }, "postMessage with message ports");
+
+    promise_test(async () => {
+      var {data} = await createPortalAndLoopMessage(sameOriginUrl, {
+        type: "array-buffer-without-transfer",
+        array: [0, 1, 2, 3, 4]
+      });
+      assert_array_equals([0, 1, 2, 3, 4], new Int8Array(data.arrayBuffer));
+    }, "postMessage with array buffer without transfer");
+
+    promise_test(async () => {
+      var {data} = await createPortalAndLoopMessage(sameOriginUrl, {
+        type: "array-buffer-with-transfer",
+        array: [0, 1, 2, 3, 4]
+      });
+      assert_array_equals([0, 1, 2, 3, 4], new Int8Array(data.arrayBuffer));
+    }, "postMessage with array buffer with transfer");
+
+    promise_test(async () => {
+      var {data} = await createPortalAndLoopMessage(sameOriginUrl, {
+        type: "invalid-message"
+      });
+      assert_equals(data.errorType, "DataCloneError");
+    }, "postMessage should throw error when serialization fails");
+
+    promise_test(async () => {
+      var {data} = await createPortalAndLoopMessage(sameOriginUrl,{
+        type: "invalid-port"
+      });
+      assert_equals(data.errorType, "TypeError");
+    }, "postMessage with invalid transferable should throw error");
+
+    promise_test(async () => {
+      assert_implements("HTMLPortalElement" in self);
+       var receiveMessage = new Promise((resolve, reject) => {
+         var bc = new BroadcastChannel("portal-host-post-message-after-activate");
+         bc.onmessage = e => { resolve(e); };
+       });
+       const portalUrl = encodeURIComponent(
+          "portal-host-post-message-after-activate.html");
+       window.open(`resources/portal-embed-and-activate.html?url=${portalUrl}`);
+       var message = await receiveMessage;
+       assert_equals(message.data, "InvalidStateError");
+    }, "Calling postMessage after receiving onactivate event should fail");
+
+    promise_test(() => {
+      assert_implements("HTMLPortalElement" in self);
+      var portal = document.createElement("portal");
+      portal.src = "resources/portal-host-post-message-navigate-1.html";
+      var count = 0;
+      var waitForMessages = new Promise((resolve, reject) => {
+        portal.addEventListener("message", e => {
+          count++;
+          if (count == 2)
+            resolve();
+        });
+      });
+      document.body.appendChild(portal);
+      return waitForMessages;
+    }, "postMessage before and after portal navigation should work");
+
+    const TIMEOUT_DURATION_MS = 1000;
+
+    promise_test(t => new Promise((resolve, reject) => {
+      const portal = document.createElement('portal');
+      portal.src = crossOriginUrl;
+      portal.onmessage = () => reject('should not have received message');
+      document.body.appendChild(portal);
+      t.step_timeout(resolve, TIMEOUT_DURATION_MS);
+    }), "postMessage from portal host in cross-origin-portal should be blocked");
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-navigate-after-adoption.html b/testing/web-platform/tests/portals/portals-navigate-after-adoption.html
new file mode 100644
index 0000000000..1ca1cfb79f
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-navigate-after-adoption.html
@@ -0,0 +1,41 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/open-blank-host.js"></script>
+<script>
+function nextMessage(target) {
+  return new Promise((resolve, reject) => {
+    target.addEventListener('message', e => resolve(e), {once: true});
+  });
+}
+
+async function openPortalAndActivate(logic) {
+  let {port1, port2} = new MessageChannel();
+  const w = await openBlankPortalHost();
+  try {
+    const portal = w.document.createElement('portal');
+    portal.src = new URL('resources/eval-portal.html?logic=' + encodeURIComponent(logic), location.href);
+    w.document.body.appendChild(portal);
+    assert_equals((await nextMessage(portal)).data, 'ready');
+    const replyPromise = nextMessage(port2);
+    await portal.activate({data: {replyPort: port1}, transfer: [port1]});
+    port2.start();
+    return (await nextMessage(port2)).data;
+  } finally {
+    w.close();
+  }
+}
+
+promise_test(async () => {
+  assert_implements("HTMLPortalElement" in self);
+  let messageFromNewSrc = await openPortalAndActivate(
+      'let predecessor = event.adoptPredecessor();' +
+      'let readyPromise = new Promise((resolve, reject) => {' +
+      '  predecessor.onmessage = e => resolve(e.data + " via new src");' +
+      '});' +
+      'predecessor.src = "/portals/resources/eval-portal.html";' +
+      'document.body.appendChild(predecessor);' +
+      'return readyPromise;');
+  assert_equals(messageFromNewSrc, 'ready via new src');
+}, "can set portal src during portalactivate");
+</script>
diff --git a/testing/web-platform/tests/portals/portals-nested.html b/testing/web-platform/tests/portals/portals-nested.html
new file mode 100644
index 0000000000..b4b396ff8d
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-nested.html
@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+  <script>
+    promise_test(() => {
+      assert_implements("HTMLPortalElement" in self);
+      var portal = document.createElement("portal");
+      portal.src = "resources/portals-nested-portal.html";
+      document.body.appendChild(portal);
+      var waitForMessage = new Promise((resolve, reject) => {
+        portal.onmessage = resolve;
+      });
+      return waitForMessage;
+    }, "nested portals shouldn't crash");
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-no-frame-crash.html b/testing/web-platform/tests/portals/portals-no-frame-crash.html
new file mode 100644
index 0000000000..cc94a772c3
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-no-frame-crash.html
@@ -0,0 +1,30 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<script>
+  test(() => {
+    let portal = document.createElement("portal");
+    let xmlDoc = document.implementation.createDocument("", null);
+    xmlDoc.appendChild(portal);
+  }, "inserting a portal element into an XML document shouldn't crash or throw");
+
+  test(() => {
+    let iframe = document.createElement("iframe");
+    document.body.appendChild(iframe);
+    let doc = iframe.contentDocument;
+    iframe.remove();
+    let portal = document.createElement("portal");
+    doc.body.appendChild(portal);
+  }, "inserting a portal element into a detached iframe's document shouldn't crash or throw");
+
+  test(() => {
+    let iframe = document.createElement("iframe");
+    document.body.appendChild(iframe);
+    let doc = iframe.contentDocument;
+    iframe.remove();
+    let portal = doc.createElement("portal");
+    doc.body.appendChild(portal);
+  }, "creating a portal element with a detached iframe's document shouldn't crash or throw");
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-post-message.sub.html b/testing/web-platform/tests/portals/portals-post-message.sub.html
new file mode 100644
index 0000000000..d556dd43d8
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-post-message.sub.html
@@ -0,0 +1,189 @@
+<!DOCTYPE html>
+<title>Test postMessage on HTMLPortalElement</title>
+<meta name="timeout" content="long">
+<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>
+<script src="resources/stash-utils.sub.js"></script>
+<script src="/common/utils.js"></script>
+<body>
+  <input id="input"/>
+  <script>
+    const sameOriginUrl = "resources/portal-post-message-portal.html"
+    const crossOriginUrl = "http://{{hosts[alt][www]}}:{{ports[http][0]}}/portals/resources/portal-post-message-x-origin-portal.html"
+
+    async function createAndInsertPortal(portalSrc) {
+      assert_implements("HTMLPortalElement" in self);
+      var portal = document.createElement("portal");
+      portal.src = portalSrc;
+      document.body.append(portal);
+
+      var loadPromise = new Promise((resolve, reject) => {
+        portal.onload = resolve;
+      });
+      await loadPromise;
+      return portal;
+    }
+
+    function postMessage(portal, ...postMessageArgs) {
+      return new Promise((resolve, reject) => {
+        portal.postMessage(...postMessageArgs);
+        portal.onmessage = e => { resolve(e.data); };
+      });
+    }
+
+    function postMessageWithMessagePorts(portal, message) {
+      return new Promise((resolve, reject) => {
+        var channel = new MessageChannel();
+        channel.port1.onmessage = e => {
+          channel.port1.close();
+          resolve(e.data);
+        };
+        portal.postMessage(message, {transfer: [channel.port2]});
+      });
+    }
+
+    promise_test(async () => {
+      var portal = await createAndInsertPortal(sameOriginUrl);
+      var message = "test message";
+      var {origin, data, sourceIsPortalHost} = await postMessage(portal, message);
+      assert_equals(data, message);
+      assert_equals(origin, window.location.origin);
+      assert_true(sourceIsPortalHost);
+    }, "postMessage message received by portalHost");
+
+    promise_test(async () => {
+      var portal = await createAndInsertPortal(sameOriginUrl);
+      var message = {
+        prop1: "value1",
+        prop2: 2.5,
+        prop3: [1, 2, "3"],
+        prop4: {
+          prop4_1: "value4_1"
+        }
+      }
+      var {data} = await postMessage(portal, message);
+      assert_object_equals(data, message);
+    }, "postMessage with message object");
+
+    promise_test(async () => {
+      var portal = await createAndInsertPortal(sameOriginUrl);
+      var message = "test message";
+      var {data} = await postMessageWithMessagePorts(portal, message);
+      assert_equals(data, message);
+    }, "postMessage with message ports and same-origin portal");
+
+    promise_test(async () => {
+      var portal = await createAndInsertPortal(sameOriginUrl);
+      var arrayBuffer = new ArrayBuffer(5);
+      var int8View = new Int8Array(arrayBuffer);
+      for (var i = 0; i < int8View.length; i++)
+        int8View[i] = i;
+      var message = {
+        arrayBuffer: arrayBuffer
+      };
+      var {data} = await postMessage(portal, message);
+      assert_array_equals([0, 1, 2, 3, 4], int8View);
+      assert_array_equals([0, 1, 2, 3, 4], data.array);
+    }, "postMessage with array buffer without transfer");
+
+    promise_test(async () => {
+      var portal = await createAndInsertPortal(sameOriginUrl);
+      var arrayBuffer = new ArrayBuffer(5);
+      var int8View = new Int8Array(arrayBuffer);
+      for (var i = 0; i < int8View.length; i++)
+        int8View[i] = i;
+      var message = {
+        arrayBuffer: arrayBuffer
+      };
+      var {data} = await postMessage(portal, message, {transfer: [arrayBuffer]});
+      assert_equals(int8View.length, 0);
+      assert_array_equals(data.array, [0, 1, 2, 3, 4]);
+    }, "postMessage with transferred array buffer");
+
+    promise_test(async t => {
+      var portal = await createAndInsertPortal(sameOriginUrl);
+
+      var {gotUserActivation} = await postMessage(portal, "test");
+      assert_false(gotUserActivation);
+
+      var {gotUserActivation, userActivation} = await postMessage(portal, "test", {includeUserActivation: true});
+      assert_true(gotUserActivation);
+      assert_false(userActivation.isActive);
+      assert_false(userActivation.hasBeenActive);
+
+      await test_driver.click(document.getElementById("input"));
+      assert_true(navigator.userActivation.isActive);
+      assert_true(navigator.userActivation.hasBeenActive);
+
+      var {userActivation} = await postMessage(portal, "test", {includeUserActivation: true});
+      assert_true(userActivation.isActive, "should have sent gesture");
+      assert_true(userActivation.hasBeenActive);
+    }, "postMessage with includeUserActivation");
+
+    promise_test(async t => {
+      var portal = document.createElement("portal");
+      return promise_rejects_dom(t, "InvalidStateError",
+                             postMessage(portal, "test message"));
+    }, "cannot call postMessage on portal without portal browsing context");
+
+    promise_test(async t => {
+      var portal = await createAndInsertPortal(sameOriginUrl);
+      return promise_rejects_dom(t, "DataCloneError",
+                             postMessage(portal, document.body));
+    }, "postMessage should fail if message serialization fails");
+
+    promise_test(async t => {
+      var portal = await createAndInsertPortal(sameOriginUrl);
+      return promise_rejects_js(t, TypeError,
+                             postMessage(portal, "test", {transfer: [null]}));
+    }, "postMessage should fail with invalid ports");
+
+    async function waitForMessage(channelName) {
+      var bc = new BroadcastChannel(channelName);
+      return new Promise((resolve, reject) => {
+        bc.onmessage = e => {
+          bc.close();
+          resolve(e.data);
+        }
+      });
+    }
+
+    promise_test(async t => {
+      assert_implements("HTMLPortalElement" in self);
+      window.open("resources/portal-post-message-before-activate-window.html");
+      let {postMessageTS, activateTS} = await waitForMessage(
+          "portals-post-message-before-activate");
+      assert_less_than_equal(postMessageTS, activateTS);
+    }, "postMessage before activate should work and preserve order");
+
+    promise_test(async t => {
+      assert_implements("HTMLPortalElement" in self);
+      window.open("resources/portal-post-message-during-activate-window.html");
+      let error = await waitForMessage("portals-post-message-during-activate");
+      assert_equals(error, "InvalidStateError");
+    }, "postMessage during activate throws error");
+
+    promise_test(async t => {
+      assert_implements("HTMLPortalElement" in self);
+      window.open("resources/portal-post-message-after-activate-window.html");
+      let error = await waitForMessage("portals-post-message-after-activate");
+      assert_equals(error, "InvalidStateError");
+    }, "postMessage after activate throws error");
+
+    const TIMEOUT_DURATION_MS = 1000;
+
+    promise_test(async t => {
+      const key = token();
+      const portal = await createAndInsertPortal(`${crossOriginUrl}?key=${key}`);
+      portal.postMessage('test message');
+      t.step_timeout(() => {
+        StashUtils.putValue(key, 'passed');
+      }, TIMEOUT_DURATION_MS);
+      const result = await StashUtils.takeValue(key);
+      assert_equals(result, 'passed');
+    }, 'postMessage should be blocked for cross-origin portals');
+
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-referrer-inherit-header.html b/testing/web-platform/tests/portals/portals-referrer-inherit-header.html
new file mode 100644
index 0000000000..1fbd88893e
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-referrer-inherit-header.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<script>
+promise_test(async () => {
+  assert_implements('HTMLPortalElement' in self, 'HTMLPortalElement is required for this test');
+  let portal = document.createElement('portal');
+  let referrerPromise = new Promise((resolve, reject) => {
+    portal.addEventListener('message', e => resolve(e.data), {once: true});
+  });
+  portal.src = 'resources/postmessage-referrer.sub.html';
+  document.body.appendChild(portal);
+  try {
+    let {httpReferrer, documentReferrer} = await referrerPromise;
+    assert_equals(httpReferrer, 'no-http-referrer', 'No HTTP Referer header should be sent');
+    assert_equals(documentReferrer, 'no-document-referrer', 'No document.referrer should be present');
+  } finally {
+    document.body.removeChild(portal);
+  }
+}, "portal contents should be loaded with no referrer if document requests it");
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-referrer-inherit-header.html.headers b/testing/web-platform/tests/portals/portals-referrer-inherit-header.html.headers
new file mode 100644
index 0000000000..7ffbf17d6b
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-referrer-inherit-header.html.headers
@@ -0,0 +1 @@
+Referrer-Policy: no-referrer
diff --git a/testing/web-platform/tests/portals/portals-referrer-inherit-meta.html b/testing/web-platform/tests/portals/portals-referrer-inherit-meta.html
new file mode 100644
index 0000000000..e77894cfa4
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-referrer-inherit-meta.html
@@ -0,0 +1,24 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<meta name="referrer" content="no-referrer">
+<body>
+<script>
+promise_test(async () => {
+  assert_implements('HTMLPortalElement' in self, 'HTMLPortalElement is required for this test');
+  let portal = document.createElement('portal');
+  let referrerPromise = new Promise((resolve, reject) => {
+    portal.addEventListener('message', e => resolve(e.data), {once: true});
+  });
+  portal.src = 'resources/postmessage-referrer.sub.html';
+  document.body.appendChild(portal);
+  try {
+    let {httpReferrer, documentReferrer} = await referrerPromise;
+    assert_equals(httpReferrer, 'no-http-referrer', 'No HTTP Referer header should be sent');
+    assert_equals(documentReferrer, 'no-document-referrer', 'No document.referrer should be present');
+  } finally {
+    document.body.removeChild(portal);
+  }
+}, "portal contents should be loaded with no referrer if document requests it");
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-referrer.html b/testing/web-platform/tests/portals/portals-referrer.html
new file mode 100644
index 0000000000..4cd3b90895
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-referrer.html
@@ -0,0 +1,61 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<script>
+promise_test(async () => {
+  assert_implements('HTMLPortalElement' in self, 'HTMLPortalElement is required for this test');
+  let portal = document.createElement('portal');
+  let referrerPromise = new Promise((resolve, reject) => {
+    portal.addEventListener('message', e => resolve(e.data), {once: true});
+  });
+  portal.src = 'resources/postmessage-referrer.sub.html';
+  document.body.appendChild(portal);
+  try {
+    let {httpReferrer, documentReferrer} = await referrerPromise;
+    assert_equals(httpReferrer, location.href, 'HTTP Referer header should be sent by default');
+    assert_equals(documentReferrer, location.href, 'document.referrer should be present by default');
+  } finally {
+    document.body.removeChild(portal);
+  }
+}, "portal contents should be loaded with referrer");
+
+promise_test(async () => {
+  assert_implements('HTMLPortalElement' in self, 'HTMLPortalElement is required for this test');
+  let portal = document.createElement('portal');
+  portal.referrerPolicy = 'no-referrer';
+  let referrerPromise = new Promise((resolve, reject) => {
+    portal.addEventListener('message', e => resolve(e.data), {once: true});
+  });
+  portal.src = 'resources/postmessage-referrer.sub.html';
+  document.body.appendChild(portal);
+  try {
+    let {httpReferrer, documentReferrer} = await referrerPromise;
+    assert_equals(httpReferrer, 'no-http-referrer', 'No HTTP Referer header should be sent');
+    assert_equals(documentReferrer, 'no-document-referrer', 'No document.referrer should be present');
+  } finally {
+    document.body.removeChild(portal);
+  }
+}, "portal contents should be loaded with no referrer if referrerpolicy=no-referrer");
+
+promise_test(async () => {
+  assert_implements('HTMLPortalElement' in self, 'HTMLPortalElement is required for this test');
+  let portal = document.createElement('portal');
+  portal.referrerPolicy = 'origin';
+  let referrerPromise = new Promise((resolve, reject) => {
+    portal.addEventListener('message', e => resolve(e.data), {once: true});
+  });
+  portal.src = 'resources/postmessage-referrer.sub.html';
+  document.body.appendChild(portal);
+  try {
+    let {httpReferrer, documentReferrer} = await referrerPromise;
+    assert_equals(httpReferrer, location.origin + '/', 'HTTP Referer header should contain origin');
+    assert_equals(documentReferrer, location.origin + '/', 'document.referrer should contain origin');
+  } finally {
+    document.body.removeChild(portal);
+  }
+}, "portal contents should be loaded with origin only if referrerpolicy=origin");
+
+// This is not exhaustive coverage of all possible policies, which are tested elsewhere.
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/portals-rendering.html b/testing/web-platform/tests/portals/portals-rendering.html
new file mode 100644
index 0000000000..229dacf4e6
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-rendering.html
@@ -0,0 +1,22 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<title>Portals rendering test</title>
+<link rel="match" href="references/portals-rendering.html">
+<body></body>
+<script>
+if (!("HTMLPortalElement" in self)) {
+  document.body.textContent = "PRECONDITION FAILED";
+  document.documentElement.classList.remove('reftest-wait');
+} else {
+  var portal = document.createElement('portal');
+  portal.src = 'resources/portals-rendering-portal.html';
+  portal.style = 'background-color: red; width: 100px; height: 100px';
+  portal.onmessage = e => {
+    window.requestAnimationFrame(function(ts) {
+      document.documentElement.classList.remove('reftest-wait');
+    });
+  };
+  document.body.appendChild(portal);
+}
+</script>
+
diff --git a/testing/web-platform/tests/portals/portals-repeated-activate.html b/testing/web-platform/tests/portals/portals-repeated-activate.html
new file mode 100644
index 0000000000..f2f36cb768
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-repeated-activate.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+  async_test(t => {
+    assert_implements("HTMLPortalElement" in self);
+    let win = window.open("resources/portal-repeated-activate-window.html");
+    win.onload = () => win.activate();
+    window.onmessage = t.step_func_done(() => {});
+  }, "test activation in page that has been reactivated")
+</script>
diff --git a/testing/web-platform/tests/portals/portals-set-src-after-activate.html b/testing/web-platform/tests/portals/portals-set-src-after-activate.html
new file mode 100644
index 0000000000..e485ef4d51
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-set-src-after-activate.html
@@ -0,0 +1,38 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/open-blank-host.js"></script>
+<script>
+function nextMessage(target) {
+  return new Promise((resolve, reject) => {
+    target.addEventListener('message', e => resolve(e), {once: true});
+  });
+}
+
+promise_test(async () => {
+  assert_implements("HTMLPortalElement" in self);
+  const w = await openBlankPortalHost();
+  try {
+    const portal = w.document.createElement('portal');
+    portal.src = new URL('resources/simple-portal-adopts-predecessor.html', location.href);
+    w.document.body.appendChild(portal);
+    assert_equals((await nextMessage(portal)).data, 'ready');
+
+    // Intentionally don't await activation finishing; this should work
+    // even if activation is ongoing.
+    let activateDone = portal.activate();
+
+    // TODO(jbroman): It shouldn't be necessary to reinsert the element to
+    // navigate it again, either.
+    w.document.body.removeChild(portal);
+    portal.src = new URL('resources/simple-portal.html', location.href);
+    w.document.body.appendChild(portal);
+    assert_equals((await nextMessage(portal)).data, 'ready');
+
+    // But activation should still resolve, eventually.
+    await activateDone;
+  } finally {
+    w.close();
+  }
+}, "Tests that a portal element can be fully reused after activate has detached it");
+</script>
diff --git a/testing/web-platform/tests/portals/predecessor-fires-unload.html b/testing/web-platform/tests/portals/predecessor-fires-unload.html
new file mode 100644
index 0000000000..cb6d98c01d
--- /dev/null
+++ b/testing/web-platform/tests/portals/predecessor-fires-unload.html
@@ -0,0 +1,40 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/open-blank-host.js"></script>
+<script>
+function nextEvent(target, type) {
+  return new Promise((resolve, reject) => target.addEventListener(type, e => resolve(e), {once: true}));
+}
+
+function timePasses(delay) {
+  return new Promise((resolve, reject) => step_timeout(() => resolve(), delay));
+}
+
+promise_test(async () => {
+  assert_implements("HTMLPortalElement" in self);
+  const w = await openBlankPortalHost();
+  try {
+    const portal = w.document.createElement('portal');
+    portal.src = new URL('resources/simple-portal.html', location.href);
+    w.document.body.appendChild(portal);
+    await nextEvent(portal, 'load');
+    const pagehideFired = nextEvent(w, 'pagehide');
+    const unloadFired = nextEvent(w, 'unload');
+    await portal.activate();
+    assert_true((await pagehideFired) instanceof w.PageTransitionEvent);
+    assert_true((await unloadFired) instanceof w.Event);
+  } finally {
+    w.close();
+  }
+}, "pagehide and unload should fire if the predecessor is not adopted");
+
+promise_test(async () => {
+  assert_implements("HTMLPortalElement" in self);
+  localStorage.setItem('predecessor-fires-unload-events', '');
+  window.open('resources/predecessor-fires-unload-watch-unload.html', '_blank', 'noopener');
+  while (localStorage.getItem('predecessor-fires-unload-events') != 'pagehide unload') {
+    await timePasses(50);
+  }
+}, "pagehide and unload should fire if the predecessor is not adopted, even without a window/opener association");
+</script>
diff --git a/testing/web-platform/tests/portals/references/portals-rendering.html b/testing/web-platform/tests/portals/references/portals-rendering.html
new file mode 100644
index 0000000000..4a8414ab56
--- /dev/null
+++ b/testing/web-platform/tests/portals/references/portals-rendering.html
@@ -0,0 +1,5 @@
+<!DOCTYPE html>
+<title>Portals rendering test</title>
+<body>
+  <div style="background-color: green; width: 100px; height: 100px">
+</body>
diff --git a/testing/web-platform/tests/portals/resources/attempt-portal-load.html b/testing/web-platform/tests/portals/resources/attempt-portal-load.html
new file mode 100644
index 0000000000..183178006f
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/attempt-portal-load.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<body>
+<script>
+portalLoaded = new Promise((resolve, reject) => {
+  let portal = document.createElement('portal');
+  portal.src = 'simple-portal.html';
+  portal.onload = resolve;
+  document.body.appendChild(portal);
+});
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/blank-host.html b/testing/web-platform/tests/portals/resources/blank-host.html
new file mode 100644
index 0000000000..d9f3a61eb8
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/blank-host.html
@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<!--
+  This is a blank page used when a test needs a new window to host and activate
+  a portal. Tests cannot simply use window.open() without a URL as about:blank
+  may not host a portal.
+-->
+<body>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/eval-portal.html b/testing/web-platform/tests/portals/resources/eval-portal.html
new file mode 100644
index 0000000000..a473501b01
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/eval-portal.html
@@ -0,0 +1,10 @@
+<!DOCTYPE html>
+<script>
+let logic = new Function('event', (new URL(location)).searchParams.get('logic'));
+onload = () => window.portalHost.postMessage('ready');
+onportalactivate = event => {
+  Promise.resolve(event)
+      .then(logic)
+      .then(reply => event.data.replyPort.postMessage(reply));
+};
+</script>
diff --git a/testing/web-platform/tests/portals/resources/focus-page-with-autofocus.html b/testing/web-platform/tests/portals/resources/focus-page-with-autofocus.html
new file mode 100644
index 0000000000..d498ef6335
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/focus-page-with-autofocus.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<body>
+  <button id="one">one</button>
+  <button id="two" autofocus>two</button>
+  <button id="three">three</button>
+  <script>
+    function messageHandler(e) {
+      if (e.data === 'check-active-element') {
+        window.requestAnimationFrame(() => {
+          let autofocusedButton = document.querySelector('#two');
+          e.source.postMessage(document.activeElement === autofocusedButton);
+        });
+      }
+    }
+
+    window.portalHost.onmessage = messageHandler;
+    window.onportalactivate = e => {
+      let portal = e.adoptPredecessor();
+      portal.onmessage = messageHandler;
+      document.body.appendChild(portal);
+    }
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/focus-page-with-button.html b/testing/web-platform/tests/portals/resources/focus-page-with-button.html
new file mode 100644
index 0000000000..81ed5465ab
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/focus-page-with-button.html
@@ -0,0 +1,35 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    function handleMessage(e) {
+      if (e.data == "focus") {
+        let button = document.querySelector("button");
+        button.onfocus = () => e.source.postMessage({focused: true}, {targetOrigin: "*"});
+        button.focus();
+      }
+
+      if (e.data == "focus-update-active-element") {
+        let button = document.querySelector("button");
+        button.focus();
+        e.source.postMessage({activeElementUpdated: document.activeElement === button}, {targetOrigin: "*"});
+      }
+    }
+
+    if (window.portalHost)
+      window.portalHost.onmessage = handleMessage;
+
+    window.onmessage = handleMessage;
+
+    window.onportalactivate = e => {
+      let portal = e.adoptPredecessor();
+      document.body.appendChild(portal);
+      portal.onmessage = handleMessage;
+    };
+
+    window.onfocus = () => {
+      if (window.portalHost)
+        window.portalHost.postMessage("window focused");
+    };
+  </script>
+  <button>A</button>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/focus-page-with-x-origin-iframe.sub.html b/testing/web-platform/tests/portals/resources/focus-page-with-x-origin-iframe.sub.html
new file mode 100644
index 0000000000..df7974e75b
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/focus-page-with-x-origin-iframe.sub.html
@@ -0,0 +1,28 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    async function handleMessage(e) {
+      if (e.data == "focus" || e.data == "focus-update-active-element") {
+        let iframe = document.querySelector("iframe");
+        iframe.contentWindow.postMessage(e.data, "*");
+      }
+    }
+
+    if (window.portalHost)
+      window.portalHost.onmessage = handleMessage;
+
+    window.onportalactivate = e => {
+      var portal = e.adoptPredecessor();
+      document.body.appendChild(portal);
+      portal.onmessage = handleMessage;
+    }
+
+    window.onmessage = e => {
+      if (window.portalHost)
+        window.portalHost.postMessage(e.data);
+      else
+        document.querySelector("portal").postMessage(e.data);
+    }
+  </script>
+  <iframe src="http://{{hosts[alt][www]}}:{{ports[http][0]}}/portals/resources/focus-page-with-button.html"></iframe>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/invalid.asis b/testing/web-platform/tests/portals/resources/invalid.asis
new file mode 100644
index 0000000000..20f7c7f7e5
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/invalid.asis
@@ -0,0 +1 @@
+This is an invalid HTTP response used to produce a network error.
diff --git a/testing/web-platform/tests/portals/resources/open-blank-host.js b/testing/web-platform/tests/portals/resources/open-blank-host.js
new file mode 100644
index 0000000000..f7580bd152
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/open-blank-host.js
@@ -0,0 +1,14 @@
+// Portal tests often need to create portals in a context other than the one
+// in which the tests are running. This is because the host context may be
+// discarded during the course of the test.
+
+// Opens a blank page for use as a portal host.
+// Tests cannot simply use window.open() without a URL as about:blank may not
+// host a portal.
+async function openBlankPortalHost() {
+  let hostWindow = window.open('/portals/resources/blank-host.html');
+  await new Promise((resolve) => {
+    hostWindow.addEventListener('load', resolve, {once: true});
+  });
+  return hostWindow;
+}
diff --git a/testing/web-platform/tests/portals/resources/portal-activate-broadcastchannel.html b/testing/web-platform/tests/portals/resources/portal-activate-broadcastchannel.html
new file mode 100644
index 0000000000..b922afaec2
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-activate-broadcastchannel.html
@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<script>
+onportalactivate = e => {
+  let bc = new BroadcastChannel(new URL(location).searchParams.get('bc'));
+  bc.postMessage({event: 'portalactivate', data: e.data});
+  bc.close();
+};
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portal-activate-data-portal.html b/testing/web-platform/tests/portals/resources/portal-activate-data-portal.html
new file mode 100644
index 0000000000..0842ad82ef
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-activate-data-portal.html
@@ -0,0 +1,9 @@
+<!DOCTYPE html>
+<script>
+let logic = new Function('event', (new URL(location)).searchParams.get('logic'));
+onload = () => window.portalHost.postMessage('ready');
+onportalactivate = event => {
+  var portal = event.adoptPredecessor();
+  portal.postMessage(logic(event));
+};
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portal-activate-event-portal.html b/testing/web-platform/tests/portals/resources/portal-activate-event-portal.html
new file mode 100644
index 0000000000..6de5aafca7
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-activate-event-portal.html
@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<title>Tests that the PortalActivateEvent is dispatched when a portal is activated</title>
+<script>
+  var test = (new URL(location)).searchParams.get("test");
+
+  function portalActivate(e) {
+    var bc = new BroadcastChannel("test-" + test);
+    bc.postMessage("passed");
+    bc.close();
+  }
+
+  if (test == "bodyeventhandler") {
+    document.write('<body onportalactivate="portalActivate()"></body>');
+  } else if (test == "eventhandler") {
+    window.onportalactivate = portalActivate;
+  } else if (test == "eventlistener") {
+    window.addEventListener("portalactivate", portalActivate);
+  }
+
+  window.portalHost.postMessage("loaded");
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portal-activate-in-handler.html b/testing/web-platform/tests/portals/resources/portal-activate-in-handler.html
new file mode 100644
index 0000000000..746ffa2b39
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-activate-in-handler.html
@@ -0,0 +1,51 @@
+<!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-vendor.js"></script>
+  </head>
+  <body>
+  </body>
+  <script>
+    // This page is reused with a different query parameter indicating which
+    // handler to register and activate a portal from.
+    const handler_name = window.location.search.substring(1);
+
+    const portal_element = document.createElement('portal');
+    portal_element.src = 'simple-portal.html';
+    document.body.appendChild(portal_element);
+
+    let page_loaded = false;
+    let portal_loaded = false;
+
+    function notifyReady() {
+      if (page_loaded && portal_loaded) {
+        window.opener.postMessage('done', '*');
+      }
+    }
+
+    portal_element.addEventListener('load', () => {
+      portal_loaded = true;
+      notifyReady();
+    });
+
+    window.addEventListener('load', () => {
+      page_loaded = true;
+      notifyReady();
+    });
+
+    // This will be used to let the parent page know the handler has run and
+    // |portal_promise| is now valid.
+    window.opener.handler_called_promise = new Promise((resolve) => {
+      window.addEventListener(handler_name, () => {
+        window.opener.portal_promise = portal_element.activate();
+
+        // Let the parent page know it can now look at |portal_promise|.
+        resolve();
+      }, {once: true});
+    });
+
+  </script>
+</html>
diff --git a/testing/web-platform/tests/portals/resources/portal-activate-inside-portal.html b/testing/web-platform/tests/portals/resources/portal-activate-inside-portal.html
new file mode 100644
index 0000000000..ff8bead324
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-activate-inside-portal.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    var portal = document.createElement("portal");
+    portal.src = "simple-portal.html";
+    portal.onload = () => {
+      portal.activate().catch(e => window.portalHost.postMessage(e.name));
+    }
+    document.body.appendChild(portal);
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portal-activate-twice-window-1.html b/testing/web-platform/tests/portals/resources/portal-activate-twice-window-1.html
new file mode 100644
index 0000000000..fbc5a6e93d
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-activate-twice-window-1.html
@@ -0,0 +1,12 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    var portal = document.createElement("portal");
+    portal.src = "simple-portal.html"
+    portal.onload = () => {
+      portal.activate();
+      portal.activate().catch(e => window.opener.postMessage(e.name, "*"));
+    }
+    document.body.append(portal);
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portal-activate-twice-window-2.html b/testing/web-platform/tests/portals/resources/portal-activate-twice-window-2.html
new file mode 100644
index 0000000000..6ba8dc5839
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-activate-twice-window-2.html
@@ -0,0 +1,22 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    var portal1 = document.createElement("portal");
+    portal1.src = "simple-portal.html"
+    var portal2 = document.createElement("portal");
+    portal2.src = "simple-portal.html"
+
+    var waitForPortalToLoad = portal => new Promise((resolve, reject) => {
+      portal.onload = resolve;
+    });
+
+    Promise.all([waitForPortalToLoad(portal1),
+                 waitForPortalToLoad(portal2)]).then(() => {
+      portal1.activate();
+      portal2.activate().catch(e => window.opener.postMessage(e.name, "*"));
+    });
+
+    document.body.append(portal1);
+    document.body.append(portal2);
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portal-close-window.html b/testing/web-platform/tests/portals/resources/portal-close-window.html
new file mode 100644
index 0000000000..a12af3cd7a
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-close-window.html
@@ -0,0 +1,7 @@
+<!DOCTYPE html>
+<script>
+onload = () => {
+  window.close();
+  window.portalHost.postMessage(window.closed);
+};
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portal-embed-and-activate.html b/testing/web-platform/tests/portals/resources/portal-embed-and-activate.html
new file mode 100644
index 0000000000..04f15b7fda
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-embed-and-activate.html
@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+<!--
+  Embeds a portal (src specified by query parameter "url") and activates it after
+  receiving a message from the portal.
+-->
+</title>
+<body>
+  <script>
+    var searchParams = new URL(location).searchParams;
+    let portal = document.createElement("portal");
+    portal.src = searchParams.get("url");
+    portal.onmessage = () => { portal.activate(); }
+    document.body.appendChild(portal);
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portal-host-cross-origin-navigate.sub.html b/testing/web-platform/tests/portals/resources/portal-host-cross-origin-navigate.sub.html
new file mode 100644
index 0000000000..26f655a0db
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-host-cross-origin-navigate.sub.html
@@ -0,0 +1,7 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    let key = (new URLSearchParams(window.location.search)).get('key');
+    window.location.href = `http://{{hosts[alt][www]}}:{{ports[http][0]}}/portals/resources/portal-host.html?key=${key}`;
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portal-host-hidden-after-activation-portal.html b/testing/web-platform/tests/portals/resources/portal-host-hidden-after-activation-portal.html
new file mode 100644
index 0000000000..491d184f97
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-host-hidden-after-activation-portal.html
@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<script>
+  window.addEventListener("portalactivate", function(e) {
+    var bc = new BroadcastChannel("portals-host-hidden-after-activation");
+    bc.postMessage({ hasHost: !!window.portalHost });
+    bc.close();
+  });
+
+  var bc = new BroadcastChannel("portals-host-hidden-after-activation");
+  bc.postMessage({hasHost: !!window.portalHost });
+  bc.close();
+
+  window.portalHost.postMessage("loaded");
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portal-host-post-message-after-activate.html b/testing/web-platform/tests/portals/resources/portal-host-post-message-after-activate.html
new file mode 100644
index 0000000000..7b03ac0294
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-host-post-message-after-activate.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<script>
+  window.portalHost.postMessage("loaded");
+
+  var ph = window.portalHost;
+
+  window.onportalactivate = e => {
+    var exception_name = ""
+    try {
+      ph.postMessage("message");
+    }
+    catch (error) {
+      exception_name = error.name;
+    }
+    bc = new BroadcastChannel("portal-host-post-message-after-activate");
+    bc.postMessage(exception_name, "*");
+    bc.close();
+  };
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portal-host-post-message-navigate-1.html b/testing/web-platform/tests/portals/resources/portal-host-post-message-navigate-1.html
new file mode 100644
index 0000000000..a59144e7e1
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-host-post-message-navigate-1.html
@@ -0,0 +1,5 @@
+<!DOCTYPE html>
+<script>
+  window.portalHost.postMessage("loaded");
+  window.location.href = "portal-host-post-message-navigate-2.html"
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portal-host-post-message-navigate-2.html b/testing/web-platform/tests/portals/resources/portal-host-post-message-navigate-2.html
new file mode 100644
index 0000000000..571c4f122e
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-host-post-message-navigate-2.html
@@ -0,0 +1,4 @@
+<!DOCTYPE html>
+<script>
+  window.portalHost.postMessage("loaded");
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portal-host-post-message-x-origin.html b/testing/web-platform/tests/portals/resources/portal-host-post-message-x-origin.html
new file mode 100644
index 0000000000..6cbc7f4b88
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-host-post-message-x-origin.html
@@ -0,0 +1,4 @@
+<!DOCTYPE html>
+<script>
+  window.portalHost.postMessage('test message');
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portal-host-post-message.html b/testing/web-platform/tests/portals/resources/portal-host-post-message.html
new file mode 100644
index 0000000000..1935ee898e
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-host-post-message.html
@@ -0,0 +1,51 @@
+<!DOCTYPE html>
+<script>
+  function postMessageWithMessagePorts() {
+    var channel = new MessageChannel();
+    channel.port1.onmessage = e => {
+      e.ports[0].postMessage("received");
+    }
+    window.portalHost.postMessage("sending port", {transfer: [channel.port2]});
+  }
+
+  function postMessageWithArrayBuffer(array, withTransfer) {
+    var arrayBuffer = new Int8Array(array).buffer;
+    if (withTransfer) {
+      window.portalHost.postMessage({arrayBuffer}, {transfer: [arrayBuffer]});
+    } else {
+      window.portalHost.postMessage({arrayBuffer});
+    }
+  }
+
+  function postMessageAndCatchException(...params) {
+    try {
+      window.portalHost.postMessage(...params);
+    } catch (e) {
+      window.portalHost.postMessage({errorType: e.name});
+    }
+  }
+
+  window.portalHost.addEventListener("message", e => {
+    if (e.data.type) {
+      var type = e.data.type;
+      switch (type) {
+        case "message-port":
+          postMessageWithMessagePorts();
+          return;
+        case "array-buffer-without-transfer":
+          postMessageWithArrayBuffer(e.data.array, false);
+          return;
+        case "array-buffer-with-transfer":
+          postMessageWithArrayBuffer(e.data.array, true);
+          return;
+        case "invalid-message":
+          postMessageAndCatchException(document.body);
+          return;
+        case "invalid-port":
+          postMessageAndCatchException("", {transfer: [null]});
+          return;
+      }
+    }
+    window.portalHost.postMessage(...e.data);
+  });
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portal-host.html b/testing/web-platform/tests/portals/resources/portal-host.html
new file mode 100644
index 0000000000..e577208236
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-host.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<script src="stash-utils.sub.js"></script>
+<body>
+  <script>
+    let queryParams = new URLSearchParams(window.location.search);
+    let key = queryParams.get('key');
+    if (key) {
+      StashUtils.putValue(key, window.portalHost ? "passed" : "failed");
+    }
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portal-inside-iframe.html b/testing/web-platform/tests/portals/resources/portal-inside-iframe.html
new file mode 100644
index 0000000000..5db75d5b5f
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-inside-iframe.html
@@ -0,0 +1,4 @@
+<!DOCTYPE html>
+<body>
+  <portal id="portal" />
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portal-post-message-after-activate-window.html b/testing/web-platform/tests/portals/resources/portal-post-message-after-activate-window.html
new file mode 100644
index 0000000000..73d2c11558
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-post-message-after-activate-window.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    var portal = document.createElement("portal");
+    portal.src = "portal-post-message-portal.html";
+    document.body.appendChild(portal);
+
+    portal.onload = () => {
+      portal.activate().then(() => {
+        error = "";
+        try {
+          portal.postMessage("message");
+        }
+        catch(err) {
+          error = err.name;
+        }
+        bc = new BroadcastChannel("portals-post-message-after-activate");
+        bc.postMessage(error);
+        bc.close();
+      });
+    }
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portal-post-message-before-activate-portal.html b/testing/web-platform/tests/portals/resources/portal-post-message-before-activate-portal.html
new file mode 100644
index 0000000000..d34875f981
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-post-message-before-activate-portal.html
@@ -0,0 +1,24 @@
+<!DOCTYPE html>
+<script>
+  var postMessagePromise = new Promise((resolve, reject) => {
+    window.portalHost.addEventListener("message", () => {
+      resolve(performance.now());
+    });
+  });
+
+  var activatePromise = new Promise((resolve, reject) => {
+    window.onportalactivate = () => {
+      resolve(performance.now());
+    }
+  });
+
+  Promise.all([postMessagePromise, activatePromise])
+    .then(values => {
+      bc = new BroadcastChannel("portals-post-message-before-activate");
+      bc.postMessage({
+        postMessageTS: values[0],
+        activateTS: values[1]
+      });
+      bc.close();
+    });
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portal-post-message-before-activate-window.html b/testing/web-platform/tests/portals/resources/portal-post-message-before-activate-window.html
new file mode 100644
index 0000000000..6389829c7c
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-post-message-before-activate-window.html
@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    var portal = document.createElement("portal");
+    portal.src = "portal-post-message-before-activate-portal.html";
+    document.body.appendChild(portal);
+
+    portal.onload = () => {
+      portal.postMessage("message");
+      portal.activate();
+    }
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portal-post-message-during-activate-window.html b/testing/web-platform/tests/portals/resources/portal-post-message-during-activate-window.html
new file mode 100644
index 0000000000..6e220277d9
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-post-message-during-activate-window.html
@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    var portal = document.createElement("portal");
+    portal.src = "simple-portal.html";
+    document.body.appendChild(portal);
+
+    portal.onload = () => {
+      portal.activate();
+      error = "";
+      try {
+        portal.postMessage("message");
+      } catch (err) {
+        error = err.name;
+      }
+      bc = new BroadcastChannel("portals-post-message-during-activate");
+      bc.postMessage(error);
+      bc.close();
+    }
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portal-post-message-portal.html b/testing/web-platform/tests/portals/resources/portal-post-message-portal.html
new file mode 100644
index 0000000000..e83ae56e08
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-post-message-portal.html
@@ -0,0 +1,29 @@
+<!DOCTYPE html>
+<script>
+  window.portalHost.onmessage = e => {
+    var message = {
+      origin: e.origin,
+      data: e.data,
+      sourceIsPortalHost: e.source === window.portalHost,
+      gotUserActivation: !!e.userActivation,
+      userActivation: {
+        isActive: e.userActivation && e.userActivation.isActive,
+        hasBeenActive: e.userActivation && e.userActivation.hasBeenActive
+      }
+    };
+
+    if (e.data.arrayBuffer) {
+      message.data = {
+        array: Array.from(new Uint8Array(e.data.arrayBuffer))
+      };
+    }
+
+    if (e.ports.length > 0) {
+      e.ports[0].postMessage(message);
+      e.ports[0].close();
+      return;
+    }
+
+    window.portalHost.postMessage(message);
+  };
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portal-post-message-x-origin-portal.html b/testing/web-platform/tests/portals/resources/portal-post-message-x-origin-portal.html
new file mode 100644
index 0000000000..57631f385c
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-post-message-x-origin-portal.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<script src="stash-utils.sub.js"></script>
+<script>
+  const queryParams = new URLSearchParams(window.location.search);
+  const key = queryParams.get('key');
+  if (key) {
+    window.portalHost.onmessage = () => {
+      StashUtils.putValue(key, 'failed');
+    };
+  }
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portal-repeated-activate-window.html b/testing/web-platform/tests/portals/resources/portal-repeated-activate-window.html
new file mode 100644
index 0000000000..e716034eff
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-repeated-activate-window.html
@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+<body>
+  <portal src="simple-portal-adopts-and-activates-predecessor.html">
+  <script>
+    function activate() {
+      var portal = document.querySelector("portal");
+      portal.activate().then(() => document.body.removeChild(portal));
+    }
+
+    var count = 0;
+    window.onportalactivate = e => {
+      ++count;
+      if (count == 1) {
+        e.adoptPredecessor().activate();
+      } else {
+        window.opener.postMessage("done", "*");
+      }
+    };
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portals-adopt-predecessor-portal.html b/testing/web-platform/tests/portals/resources/portals-adopt-predecessor-portal.html
new file mode 100644
index 0000000000..b838b38be1
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portals-adopt-predecessor-portal.html
@@ -0,0 +1,77 @@
+<!doctype html>
+<script>
+  var searchParams = new URL(location).searchParams;
+  var test = searchParams.get("test");
+
+  window.onportalactivate = function(e) {
+    if (test == "adopt-once") {
+      var portal = e.adoptPredecessor();
+      document.body.appendChild(portal);
+
+      if (portal instanceof HTMLPortalElement) {
+        portal.postMessage("adopted");
+      }
+    }
+    if (test == "adopt-twice") {
+      var portal = e.adoptPredecessor();
+      document.body.appendChild(portal);
+
+      try {
+        e.adoptPredecessor();
+      } catch(e) {
+        if (e.name == "InvalidStateError") {
+          portal.postMessage("passed");
+        }
+      }
+    }
+    if (test == "adopt-after-event") {
+      setTimeout(function() {
+        try {
+          e.adoptPredecessor();
+        } catch(e) {
+          if (e.name == "InvalidStateError") {
+            var bc_test = new BroadcastChannel(`test-${test}`);
+            bc_test.postMessage("passed");
+            bc_test.close();
+          }
+        }
+      });
+    }
+    if (test == "adopt-and-activate") {
+      var portal = e.adoptPredecessor();
+      portal.activate();
+    }
+    if (test == "adopt-attach-remove") {
+      var portal = e.adoptPredecessor();
+      document.body.appendChild(portal);
+      setTimeout(() => {
+        document.body.removeChild(portal);
+        var bc_test = new BroadcastChannel(`test-${test}`);
+        bc_test.postMessage("passed");
+        bc_test.close();
+      });
+    }
+    if (test == "adopt-and-discard") {
+      var portal = e.adoptPredecessor();
+      setTimeout(() => {
+        // portal should be inactive and activate should fail.
+        portal.activate().catch(e => {
+          if (e.name == "InvalidStateError") {
+            var bc_test = new BroadcastChannel(`test-${test}`);
+            bc_test.postMessage("passed");
+            bc_test.close();
+          }
+        });
+      });
+    }
+    if (test == "adopt-to-disconnected-node") {
+      var portal = e.adoptPredecessor();
+      document.body.appendChild(portal);
+      var node = document.createElement("div");
+      node.appendChild(portal);
+      var bc_test = new BroadcastChannel(`test-${test}`);
+      bc_test.postMessage("passed");
+      bc_test.close();
+    }
+  }
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portals-adopt-predecessor.html b/testing/web-platform/tests/portals/resources/portals-adopt-predecessor.html
new file mode 100644
index 0000000000..66d47d12ac
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portals-adopt-predecessor.html
@@ -0,0 +1,20 @@
+<!doctype html>
+<body>
+</body>
+<script>
+  var searchParams = new URL(location).searchParams;
+  var test = searchParams.get("test");
+  var portal = document.createElement("portal");
+  portal.src = `portals-adopt-predecessor-portal.html?test=${test}`;
+  portal.onload = () => {
+    portal.activate().then(() => {
+      window.addEventListener("portalactivate", e => {
+        window.opener.postMessage({test, message: "passed"}, "*");
+      });
+      window.portalHost.addEventListener("message", e => {
+        window.opener.postMessage({test, message: e.data}, "*");
+      });
+    });
+  }
+  document.body.appendChild(portal);
+</script>
diff --git a/testing/web-platform/tests/portals/resources/portals-nested-portal.html b/testing/web-platform/tests/portals/resources/portals-nested-portal.html
new file mode 100644
index 0000000000..278b32eea0
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portals-nested-portal.html
@@ -0,0 +1,9 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    var portal = document.createElement("portal");
+    portal.src = "simple-portal.html";
+    portal.onload = e => window.portalHost.postMessage(e.data);
+    document.body.appendChild(portal);
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portals-rendering-portal.html b/testing/web-platform/tests/portals/resources/portals-rendering-portal.html
new file mode 100644
index 0000000000..31b3f4a990
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portals-rendering-portal.html
@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<body style="background-color: green">
+  <script>
+    window.requestAnimationFrame(function(ts) {
+      window.portalHost.postMessage("loaded");
+    });
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/postmessage-referrer.sub.html b/testing/web-platform/tests/portals/resources/postmessage-referrer.sub.html
new file mode 100644
index 0000000000..c3837dc79d
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/postmessage-referrer.sub.html
@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<script>
+  let message = {
+    httpReferrer: '{{header_or_default(Referer, no-http-referrer)}}',
+    documentReferrer: document.referrer || 'no-document-referrer',
+  };
+  window.portalHost.postMessage(message);
+</script>
diff --git a/testing/web-platform/tests/portals/resources/predecessor-fires-unload-watch-unload.html b/testing/web-platform/tests/portals/resources/predecessor-fires-unload-watch-unload.html
new file mode 100644
index 0000000000..f58da48ca1
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/predecessor-fires-unload-watch-unload.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<body>
+<script>
+function nextEvent(target, type) {
+  return new Promise((resolve, reject) => target.addEventListener(type, e => resolve(e), {once: true}));
+}
+
+onload = async function() {
+  const portal = document.createElement('portal');
+  portal.src = new URL('simple-portal.html', location.href);
+  document.body.appendChild(portal);
+  await nextEvent(portal, 'load');
+
+  let firedEvents = [];
+  for (let type of ['pagehide', 'unload']) {
+    nextEvent(window, type).then(() => {
+      firedEvents.push(type);
+      localStorage.setItem('predecessor-fires-unload-events', firedEvents.join(' '));
+    });
+  }
+
+  portal.activate();
+};
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/simple-portal-adopts-and-activates-predecessor.html b/testing/web-platform/tests/portals/resources/simple-portal-adopts-and-activates-predecessor.html
new file mode 100644
index 0000000000..56bfd10f64
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/simple-portal-adopts-and-activates-predecessor.html
@@ -0,0 +1,6 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    window.onportalactivate = e => e.adoptPredecessor().activate();
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/simple-portal-adopts-predecessor.html b/testing/web-platform/tests/portals/resources/simple-portal-adopts-predecessor.html
new file mode 100644
index 0000000000..b5ea9f029d
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/simple-portal-adopts-predecessor.html
@@ -0,0 +1,7 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    window.portalHost.postMessage("ready");
+    onportalactivate = e => document.body.appendChild(e.adoptPredecessor());
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/simple-portal.html b/testing/web-platform/tests/portals/resources/simple-portal.html
new file mode 100644
index 0000000000..7d7b678cad
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/simple-portal.html
@@ -0,0 +1,6 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    window.portalHost.postMessage("ready");
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/stash-utils.sub.js b/testing/web-platform/tests/portals/resources/stash-utils.sub.js
new file mode 100644
index 0000000000..30efe83633
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/stash-utils.sub.js
@@ -0,0 +1,43 @@
+const STASH_RESPONDER = "wss://{{host}}:{{ports[wss][0]}}/stash_responder_blocking";
+
+class StashUtils {
+  /**
+   * Sends a request to store (|key|, |tuple|) in Stash
+   * (https://web-platform-tests.org/tools/wptserve/docs/stash.html).
+   * @param {string} key A UUID that acts as a key that can be used to retrieve |value| later.
+   * @param {string} value Value to be stored in Stash.
+   * @returns {Promise} Promise that resolves once the server responds.
+   */
+  static putValue(key, value) {
+    return new Promise(resolve => {
+        const ws = new WebSocket(STASH_RESPONDER);
+        ws.onopen = () => {
+          ws.send(JSON.stringify({action: 'set', key: key, value: value}));
+        };
+        ws.onmessage = e => {
+          ws.close();
+          resolve();
+        };
+    });
+  }
+
+  /**
+   * Retrieves value associated with |key| in Stash. If no value has been
+   * associated with |key| yet, the method waits for putValue to be called with
+   * |key|, and a value to be associated, before resolving the return promise.
+   * @param {string} key A UUID that uniquely identifies the value to retrieve.
+   * @returns {Promise<string>} A promise that resolves with the value associated with |key|.
+   */
+  static takeValue(key) {
+    return new Promise(resolve => {
+      const ws = new WebSocket(STASH_RESPONDER);
+      ws.onopen = () => {
+        ws.send(JSON.stringify({action: 'get', key: key}));
+      };
+      ws.onmessage = e => {
+        ws.close();
+        resolve(JSON.parse(e.data).value);
+      };
+    });
+  }
+}
diff --git a/testing/web-platform/tests/portals/xfo/portals-xfo-deny.sub.html b/testing/web-platform/tests/portals/xfo/portals-xfo-deny.sub.html
new file mode 100644
index 0000000000..efc925276c
--- /dev/null
+++ b/testing/web-platform/tests/portals/xfo/portals-xfo-deny.sub.html
@@ -0,0 +1,43 @@
+<!DOCTYPE html>
+<meta name="timeout" content="long">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<script>
+// TODO(jbroman): Ideally these would also check that the portal element gets a
+// completion event.
+
+async_test(t => {
+  assert_implements("HTMLPortalElement" in self);
+  var portal = document.createElement('portal');
+  portal.src = "/portals/xfo/resources/xfo-deny.asis";
+  portal.onmessage = t.unreached_func("should not have received a message");
+  document.body.appendChild(portal);
+  t.add_cleanup(() => portal.remove());
+  t.step_timeout(() => t.done(), 2000);
+}, "`XFO: DENY` blocks same-origin portals.");
+
+async_test(t => {
+  assert_implements("HTMLPortalElement" in self);
+  var portal = document.createElement('portal');
+  portal.src = "http://{{domains[www]}}:{{ports[http][0]}}/portals/xfo/resources/xfo-deny.asis";
+  portal.onmessage = t.unreached_func("should not have received a message");
+  document.body.appendChild(portal);
+  t.add_cleanup(() => portal.remove());
+  t.step_timeout(() => t.done(), 2000);
+}, "`XFO: DENY` blocks cross-origin portals.");
+
+async_test(t => {
+  assert_implements("HTMLPortalElement" in self);
+  var portal = document.createElement('portal');
+  portal.src = "/portals/xfo/resources/xfo-deny.asis";
+  portal.onmessage = t.unreached_func("should not have received a message");
+  document.body.appendChild(portal);
+  t.add_cleanup(() => portal.remove());
+  t.step_timeout(async () => {
+    await promise_rejects_dom(t, 'InvalidStateError', portal.activate());
+    t.done();
+  }, 2000);
+}, "Portals blocked by `XFO: DENY` cannot be activated.");
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/xfo/portals-xfo-sameorigin.html b/testing/web-platform/tests/portals/xfo/portals-xfo-sameorigin.html
new file mode 100644
index 0000000000..2482476782
--- /dev/null
+++ b/testing/web-platform/tests/portals/xfo/portals-xfo-sameorigin.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<meta name="timeout" content="long">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/common/get-host-info.sub.js"></script>
+<body>
+<script>
+async_test(t => {
+  assert_implements("HTMLPortalElement" in self);
+  var portal = document.createElement('portal');
+  portal.src = get_host_info().HTTP_REMOTE_HOST + "/portals/xfo/resources/xfo-sameorigin.asis";
+  portal.onmessage = t.unreached_func("should not have received a message");
+  document.body.appendChild(portal);
+  t.add_cleanup(() => portal.remove());
+  t.step_timeout(() => t.done(), 2000);
+}, "`XFO: SAMEORIGIN` blocks cross-origin portals.");
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/xfo/resources/xfo-deny.asis b/testing/web-platform/tests/portals/xfo/resources/xfo-deny.asis
new file mode 100644
index 0000000000..7779830852
--- /dev/null
+++ b/testing/web-platform/tests/portals/xfo/resources/xfo-deny.asis
@@ -0,0 +1,8 @@
+HTTP/1.1 200 OK
+Content-Type: text/html
+X-Frame-Options: DENY
+
+<!DOCTYPE html>
+<script>
+window.portalHost.postMessage('loaded', '*');
+</script>
diff --git a/testing/web-platform/tests/portals/xfo/resources/xfo-sameorigin.asis b/testing/web-platform/tests/portals/xfo/resources/xfo-sameorigin.asis
new file mode 100644
index 0000000000..8f3982bd84
--- /dev/null
+++ b/testing/web-platform/tests/portals/xfo/resources/xfo-sameorigin.asis
@@ -0,0 +1,8 @@
+HTTP/1.1 200 OK
+Content-Type: text/html
+X-Frame-Options: SAMEORIGIN
+
+<!DOCTYPE html>
+<script>
+window.portalHost.postMessage('loaded', '*');
+</script>
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