IntersectionObserver: use an idle callback to send notifications.

third_party/WebKit/LayoutTests/http/tests/intersection-observer/iframe-cross-origin.html

Index: third_party/WebKit/LayoutTests/http/tests/intersection-observer/iframe-cross-origin.html
diff --git a/third_party/WebKit/LayoutTests/http/tests/intersection-observer/iframe-cross-origin.html b/third_party/WebKit/LayoutTests/http/tests/intersection-observer/iframe-cross-origin.html
index 3324515a453456a0c2648cce43c58f7226ac0b4f..290d28c088683657e3983ce06aaff35384bf3a83 100644
--- a/third_party/WebKit/LayoutTests/http/tests/intersection-observer/iframe-cross-origin.html
+++ b/third_party/WebKit/LayoutTests/http/tests/intersection-observer/iframe-cross-origin.html
@@ -53,7 +53,8 @@ function handleMessage(event) {
   } else if (event.data.hasOwnProperty('actual')) {
     checkData(event.data.actual, event.data.expected);
   } else if (event.data.hasOwnProperty('DONE')) {
-    finishJSTest();
+    // Allow time for pending idle tasks to finish to prevent leaks.
+    setTimeout(finishJSTest, 150);

[sof, 2016/03/17 07:14:58]

Do you need this with the leak exemptions and once the fix for 595155 lands? For
this & all other instances of it in this CL.

[szager1, 2016/03/17 17:43:22]

The fix for 595155 will make it possible to remove the lines from
LayoutTests/LeakExpectations, but only if the tests continue to use setTimeout
here.  To avoid leaking, the test code must be certain that all idle tasks have
completed before exiting.

Issue 595152 shows that the idle tasks scheduled by IntersectionObserver will
only run when their 100ms timeout expires, hence the slightly conservative 150ms
timeout here.  And even were 595152 fixed, we'd probably *still* need a
setTimeout here, because there's no programmatic way to ascertain whether the
idle task actually ran.

[ojan, 2016/03/17 17:48:03]

Can you instead add a callback to the IntersectionObserver and finishJSTest
inside the callback?

     document.scrollingElement.scrollTop = 0;
   } else {
     requestAnimationFrame(function () { iframe.contentWindow.postMessage("", "*") });
@@ -61,7 +62,11 @@ function handleMessage(event) {
 }
 
 window.addEventListener("message", handleMessage);
+
 iframe.onload = function() {
-  iframe.contentWindow.postMessage("", "*")
-};
+  // See LayoutTests/intersection-observer/README for explanation of double RAF.
+  requestAnimationFrame(() => {
+      requestAnimationFrame(() => { iframe.contentWindow.postMessage("", "*") })
+  });
+}
 </script>