Convert IntersectionObserver tests to use testRunner.runIdleTasks.

third_party/WebKit/LayoutTests/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.
-setPrintTestResultsLazily();
-self.jsTestIsAsync = true;
-
-function rectArea(rect) {
-  return (rect.left - rect.right) * (rect.bottom - rect.top);
-}
-
-function rectToString(rect) {
-  return "[" + rect.left + ", " + rect.right + ", " + rect.top + ", " + rect.bottom + "]";
-}
-
-function entryToString(entry) {
-  var ratio = ((entry.intersectionRect.width * entry.intersectionRect.height) /
-               (entry.boundingClientRect.width * entry.boundingClientRect.height));
-  return (
-      "boundingClientRect=" + rectToString(entry.boundingClientRect) + "\n" +
-      "intersectionRect=" + rectToString(entry.intersectionRect) + "\n" +
-      "visibleRatio=" + ratio + "\n" +
-      "rootBounds=" + rectToString(entry.rootBounds) + "\n" +
-      "target=" + entry.target + "\n" +
-      "time=" + entry.time);
-}
-
-function intersectionRatio(entry) {
-  var targetArea = rectArea(entry.boundingClientRect);
-  if (!targetArea)
-    return 0;
-  return rectArea(entry.intersectionRect) / targetArea;
-}