CSS Animations: fix flaky zoom-responsive-transform-animation.html

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

Index: third_party/WebKit/LayoutTests/animations/zoom-responsive-transform-animation.html
diff --git a/third_party/WebKit/LayoutTests/animations/zoom-responsive-transform-animation.html b/third_party/WebKit/LayoutTests/animations/zoom-responsive-transform-animation.html
index 1767b2599d9876a5e294ae67124a53a2cfea2df9..dda23df93babc63fd7dd308d91cd5481db189f07 100644
--- a/third_party/WebKit/LayoutTests/animations/zoom-responsive-transform-animation.html
+++ b/third_party/WebKit/LayoutTests/animations/zoom-responsive-transform-animation.html
@@ -14,7 +14,9 @@
 }
 </style>
 <div id="container"></div>
+<div id="footer"></div>
 <script>
+'use strict';
 [
   'perspective(200px) translate3D(10px, 10px, 10px)',
   'matrix(0, 1, 1, 0, 10, 10)',
@@ -47,12 +49,18 @@
 if (window.testRunner)
   testRunner.waitUntilDone();
 
+function waitForCompositor() {
+  return footer.animate({opacity: ['1', '1']}, 1).ready;
+}
+
 requestAnimationFrame(() => {
   requestAnimationFrame(() => {
     internals.setZoomFactor(2);
     requestAnimationFrame(() => {
-      if (window.testRunner)
-        testRunner.notifyDone();
+      waitForCompositor().then(() => {
+        if (window.testRunner)
+          testRunner.notifyDone();
+      });
     });
   });
 });