Convert IntersectionObserver tests to use testRunner.runIdleTasks.

third_party/WebKit/LayoutTests/intersection-observer/unclipped-root.html

Index: third_party/WebKit/LayoutTests/intersection-observer/unclipped-root.html
diff --git a/third_party/WebKit/LayoutTests/intersection-observer/unclipped-root.html b/third_party/WebKit/LayoutTests/intersection-observer/unclipped-root.html
index 2bb0c81f770ce185dc3840dd1e094648baa08ffa..3ad77c701904934cc480f9894f64b83ee435b594 100644
--- a/third_party/WebKit/LayoutTests/intersection-observer/unclipped-root.html
+++ b/third_party/WebKit/LayoutTests/intersection-observer/unclipped-root.html
@@ -32,19 +32,16 @@ onload = function() {
   observer.observe(target);
   entries.push(...observer.takeRecords());
   shouldBeEqualToNumber("entries.length", 0);
-  // See README for explanation of double RAF.
-  requestAnimationFrame(() => { requestAnimationFrame(step0) });
+  waitForNotification(step0);
 }
 
 function step0() {
-  entries.push(...observer.takeRecords());
   shouldBeEqualToNumber("entries.length", 0);
   target.style.transform = "translateY(195px)";
-  requestAnimationFrame(step1);
+  waitForNotification(step1);
 }
 
 function step1() {
-  entries.push(...observer.takeRecords());
   shouldBeEqualToNumber("entries.length", 1);
   if (entries.length > 0) {
     shouldBeEqualToNumber("entries[0].boundingClientRect.left", 15);