Convert IntersectionObserver tests to use testRunner.runIdleTasks.

third_party/WebKit/LayoutTests/intersection-observer/remove-element.html

Index: third_party/WebKit/LayoutTests/intersection-observer/remove-element.html
diff --git a/third_party/WebKit/LayoutTests/intersection-observer/remove-element.html b/third_party/WebKit/LayoutTests/intersection-observer/remove-element.html
index df0ed11617899d0b6d4c6a4fd07ebe7a26d85fe3..0eb53ea55c8235298050811e275362b7c6f5e35b 100644
--- a/third_party/WebKit/LayoutTests/intersection-observer/remove-element.html
+++ b/third_party/WebKit/LayoutTests/intersection-observer/remove-element.html
@@ -23,11 +23,10 @@ onload = function() {
   entries = entries.concat(observer.takeRecords());
   shouldBeEqualToNumber("entries.length", 0);
   root.scrollTop = 150;
-  requestAnimationFrame(() => { requestAnimationFrame(step1) });
+  waitForNotification(step1);
 }
 
 function step1() {
-  entries = entries.concat(observer.takeRecords());
   shouldBeEqualToNumber("entries.length", 1);
   if (entries.length > 0) {
     shouldBeEqualToNumber("entries[0].boundingClientRect.left", 11);
@@ -45,11 +44,10 @@ function step1() {
     shouldEvaluateToSameObject("entries[0].target", target);
   }
   root.removeChild(target);
-  requestAnimationFrame(step2);
+  waitForNotification(step2);
 }
 
 function step2() {
-  entries = entries.concat(observer.takeRecords());
   shouldBeEqualToNumber("entries.length", 2);
   if (entries.length > 1) {
     shouldBeEqualToNumber("entries[1].boundingClientRect.left", 0);
@@ -68,18 +66,16 @@ function step2() {
   }
   root.scrollTop = 0;
   root.insertBefore(target, afterTarget);
-  requestAnimationFrame(step3);
+  waitForNotification(step3);
 }
 
 function step3() {
-  entries = entries.concat(observer.takeRecords());
   shouldBeEqualToNumber("entries.length", 2);
   root.scrollTop = 150;
-  requestAnimationFrame(step4);
+  waitForNotification(step4);
 }
 
 function step4() {
-  entries = entries.concat(observer.takeRecords());
   shouldBeEqualToNumber("entries.length", 3);
   if (entries.length > 2) {
     shouldBeEqualToNumber("entries[2].boundingClientRect.left", 11);