1 files changed, 41 insertions, 0 deletions
diff --git a/testing/web-platform/tests/longtask-timing/longtask-in-sibling-iframe.html b/testing/web-platform/tests/longtask-timing/longtask-in-sibling-iframe.html
new file mode 100644
index 0000000000..396a9beeea
--- /dev/null
+++ b/testing/web-platform/tests/longtask-timing/longtask-in-sibling-iframe.html
@@ -0,0 +1,41 @@
+<!DOCTYPE HTML>
+<meta charset=utf-8>
+<title>LongTask Timing: long task in sibling iframe</title>
+<body>
+
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<script>
+  async_test(t => {
+    assert_implements(window.PerformanceLongTaskTiming, 'Longtasks are not supported.');
+    window.addEventListener('message', t.step_func(e => {
+      assert_equals(e.data['entryType'], 'longtask');
+      // Ignore any long task that may be produced by the top-level frame.
+      if (e.data['frame-attribution'] === 'same-origin-ancestor')
+        return;
+
+      assert_equals(e.data['frame-attribution'], 'same-origin');
+      assert_equals(e.data['task-attribution'], 'unknown');
+      assert_equals(e.data['containerType'], 'iframe');
+      assert_equals(e.data['containerId'], 'longtask-iframe-id');
+      assert_equals(e.data['containerName'], 'longtask-iframe-name');
+      assert_equals(e.data['containerSrc'], 'resources/subframe-with-longtask.html');
+      t.done();
+    }));
+    const observingFrame = document.createElement('iframe');
+    observingFrame.id = 'observing-iframe-id';
+    observingFrame.name = 'observing-iframe-name';
+    document.body.appendChild(observingFrame);
+    observingFrame.src = 'resources/subframe-observing-longtask.html'
+
+    observingFrame.onload = () => {
+      const longtaskFrame = document.createElement('iframe');
+      longtaskFrame.id = 'longtask-iframe-id';
+      longtaskFrame.name = 'longtask-iframe-name';
+      document.body.appendChild(longtaskFrame);
+      longtaskFrame.src = 'resources/subframe-with-longtask.html'
+    };
+}, 'Performance longtask entries are observable in sibling iframe.');
+</script>
+</body>