IntersectionObserver: use an idle callback to send notifications.

third_party/WebKit/LayoutTests/intersection-observer/observer-without-js-reference.html

Index: third_party/WebKit/LayoutTests/intersection-observer/observer-without-js-reference.html
diff --git a/third_party/WebKit/LayoutTests/intersection-observer/observer-without-js-reference.html b/third_party/WebKit/LayoutTests/intersection-observer/observer-without-js-reference.html
index 637a955f3c97d1c963356a5e20b30d590884e7db..f15267663aa49bc023e698e5201617d48efac682 100644
--- a/third_party/WebKit/LayoutTests/intersection-observer/observer-without-js-reference.html
+++ b/third_party/WebKit/LayoutTests/intersection-observer/observer-without-js-reference.html
@@ -6,19 +6,28 @@
 <div style="width:100%; height:700px;"></div>
 
 <script>
-  jsTestIsAsync = true;
-  description("IntersectionObserver continues to produce notifications when it has no javascript references.");
-  var target = document.getElementById("target");
-  var entries = [];
-  new IntersectionObserver(function(changes) {
-      entries.push(...changes);
-  }).observe(target);
-  gc();
-  document.scrollingElement.scrollTop = 300;
-  requestAnimationFrame(function () {
-    setTimeout(function() {
-      shouldBeEqualToNumber("entries.length", 1);
-      finishJSTest();
-    });
-  });
+jsTestIsAsync = true;
+description("IntersectionObserver continues to produce notifications when it has no javascript references.");
+var target = document.getElementById("target");
+var entries = [];
+new IntersectionObserver(function(changes) {
+    entries.push(...changes);
+}).observe(target);
+gc();
+document.scrollingElement.scrollTop = 300;
+// See README for explanation of double RAF.
+requestAnimationFrame(() => { requestAnimationFrame(() => {
+  // In other IntersectionObserver tests, observer.takeRecords() is used to ensure that
+  // all pending notifications are taken.  Because this test specifically tests the
+  // case where the observer object has no js references, it can't use takeRecords().
+  // However, the IntersectionObserver spec mandates that all notifications must be
+  // sent within 100ms of being generated, so this timeout effectively tests conformance
+  // with that requirement.
+  // TODO(szager): Switch setTimeout to testRunner.runIdleTasks after this patch lands:
+  //   https://codereview.chromium.org/1806133002/
+  setTimeout(() => {
+    shouldBeEqualToNumber("entries.length", 1);
+    finishJSTest();
+  }, 100)
+}) });
 </script>