Fix flaky zoom-responsive-transform-animation.html

We ensure the new zoom factor has been processed by the compositor,
using requestAnimationFrame and a finished promise.

BUG=743009

Change-Id: I5d6b97333d170ceaa6bcd29db3e84446ef59d18b
Reviewed-on: https://chromium-review.googlesource.com/575729Reviewed-by: nainar <nainar@chromium.org>
Commit-Queue: Eric Willigers <ericwilligers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487369}

third_party/WebKit/LayoutTests/animations/responsive/zoom-responsive-transform-animation-expected.html

@@ -53,7 +53,7 @@ if (window.testRunner)
   testRunner.waitUntilDone();
 
 function waitForCompositor() {
-  return footer.animate({opacity: ['1', '1']}, 1).ready;
+  return footer.animate({opacity: ['1', '1']}, 1).finished;
 }
 
 requestAnimationFrame(() => {

third_party/WebKit/LayoutTests/animations/responsive/zoom-responsive-transform-animation.html

@@ -50,16 +50,18 @@ if (window.testRunner)
   testRunner.waitUntilDone();
 
 function waitForCompositor() {
-  return footer.animate({opacity: ['1', '1']}, 1).ready;
+  return footer.animate({opacity: ['1', '1']}, 1).finished;
 }
 
 requestAnimationFrame(() => {
   requestAnimationFrame(() => {
     internals.setZoomFactor(2);
     requestAnimationFrame(() => {
-      waitForCompositor().then(() => {
-        if (window.testRunner)
-          testRunner.notifyDone();
+      requestAnimationFrame(() => {
+        waitForCompositor().then(() => {
+          if (window.testRunner)
+            testRunner.notifyDone();
+        });
       });
     });
   });