Convert IntersectionObserver tests to use testRunner.runIdleTasks.

third_party/WebKit/LayoutTests/intersection-observer/same-document-zero-size-target.html

Index: third_party/WebKit/LayoutTests/intersection-observer/same-document-zero-size-target.html
diff --git a/third_party/WebKit/LayoutTests/intersection-observer/same-document-zero-size-target.html b/third_party/WebKit/LayoutTests/intersection-observer/same-document-zero-size-target.html
index 51010bb73b0bd48e6234e61893464b5f84cdc767..24c3c38374d804cda539b1202906e354cf61ba48 100644
--- a/third_party/WebKit/LayoutTests/intersection-observer/same-document-zero-size-target.html
+++ b/third_party/WebKit/LayoutTests/intersection-observer/same-document-zero-size-target.html
@@ -16,12 +16,10 @@ onload = function() {
   entries.push(...observer.takeRecords());
   shouldBeEqualToNumber("entries.length", 0);
   document.scrollingElement.scrollTop = 300;
-  // See README for explanation of double RAF.
-  requestAnimationFrame(() => { requestAnimationFrame(step1) });
+  waitForNotification(step1);
 };
 
 function step1() {
-  entries.push(...observer.takeRecords());
   shouldBeEqualToNumber("entries.length", 1);
   if (entries.length > 0) {
     shouldBeEqualToNumber("entries[0].boundingClientRect.left", 8);
@@ -44,11 +42,10 @@ function step1() {
     shouldEvaluateToSameObject("entries[0].rootBounds", entries[0].rootBounds);
   }
   document.scrollingElement.scrollTop = 100;
-  requestAnimationFrame(step2);
+  waitForNotification(step2);
 }
 
 function step2() {
-  entries.push(...observer.takeRecords());
   shouldBeEqualToNumber("entries.length", 2);
   if (entries.length > 1) {
     shouldBeEqualToNumber("entries[1].boundingClientRect.left", 8);