Switch IntersectionObserver to postTask.

third_party/WebKit/LayoutTests/resources/intersection-observer-helper-functions.js

 // Some of the js-test.js boilerplate will add stuff to the top of the document early
 // enough to screw with frame offsets that are measured by the test.  Delay all that
 // jazz until the actual test code is finished.
 if (self.isJsTest) {
   setPrintTestResultsLazily();
   self.jsTestIsAsync = true;
 }
 
-// waitForNotification is a requestIdleCallback wrapped in a setTimeout wrapped in a
+// waitForNotification is a setTimeout wrapped in a setTimeout wrapped in a
 // requestAnimationFrame.  What in the wide, wide world of sports is going on here?
 //
 // Here's the order of events:
 //
 // - firstTestFunction
 //   - Change layout to generate new IntersectionObserver notifications.
 //   - waitForNotification(secondTestFunction)
 //     - requestAnimationFrame
 // - BeginFrame
 //   - requestAnimationFrame handler runs.
-//     - setTimeout
+//     - queue first setTimeout
 //   - FrameView::updateAllLifecyclePhases
 //     - IntersectionObserver generates notification based on the new layout.
-//       - Post idle task to deliver notification.
-//   - setTimeout handler runs.
-//     - testRunner.runIdleTasks or requestIdleCallback.
-//   - Idle tasks run -- more or less immediately if (self.testRunner),
-//     possibly delayed if (!self.testRunner).
+//       - Post task to deliver notification.
+//   - first setTimeout runs.
+//     - queue second setTimeout
+//   - Posted task runs.
 //     - IntersectionObserver notifications are delivered.
-//     - secondTestFunction
-//       - Verify notifications generated by firstTestFunction.
-//       - Change layout to generate new IntersectionObserver notifications.
-//       - waitForNotification(thirdTestFunction)
-//
-// Note that this should work equally well in these operation conditions:
-//
-//   - layout test using single-threaded compositing (the default)
-//   - layout test using multi-threaded compositing (virtual/threaded/)
-//   - Not in a layout test and using multi-threaded compositing (the only configuration we ship)
+//   - second setTimeout runs secondTestFunction
+//     - Verify notifications generated by firstTestFunction.
+//     - Change layout to generate new IntersectionObserver notifications.
+//     - waitForNotification(thirdTestFunction)
 function waitForNotification(f) {
   requestAnimationFrame(() => {
     setTimeout(() => {
-      if (self.testRunner)
-        testRunner.runIdleTasks(f);
-      else
-        requestIdleCallback(f);
+      setTimeout(f);
     });
   });
 }
 
 function rectToString(rect) {
   return "[" + rect.left + ", " + rect.right + ", " + rect.top + ", " + rect.bottom + "]";
 }
 
 function entryToString(entry) {
   var ratio = ((entry.intersectionRect.width * entry.intersectionRect.height) /
@@ skipping 44 matching lines @@
 
 function entryToJson(entry) {
   return {
     boundingClientRect: clientRectToJson(entry.boundingClientRect),
     intersectionRect: clientRectToJson(entry.intersectionRect),
     rootBounds: clientRectToJson(entry.rootBounds),
     time: entry.time,
     target: entry.target.id
   };
 }