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

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

Index: third_party/WebKit/LayoutTests/animations/zoom-responsive-transform-animation-expected.html
diff --git a/third_party/WebKit/LayoutTests/animations/zoom-responsive-transform-animation-expected.html b/third_party/WebKit/LayoutTests/animations/zoom-responsive-transform-animation-expected.html
index 95c25c6c9075a40f44465413edf87bf2e27fe1e5..d35fdf332072bcce721dee37e5178d5fb158664e 100644
--- a/third_party/WebKit/LayoutTests/animations/zoom-responsive-transform-animation-expected.html
+++ b/third_party/WebKit/LayoutTests/animations/zoom-responsive-transform-animation-expected.html
@@ -14,7 +14,9 @@
 }
 </style>
 <div id="container"></div>
+<div id="footer"></div>
 <script>
+'use strict';
 internals.setZoomFactor(2);
 
 [
@@ -50,10 +52,16 @@ internals.setZoomFactor(2);
 if (window.testRunner)
   testRunner.waitUntilDone();
 
+function waitForCompositor() {
+  return footer.animate({opacity: ['1', '1']}, 1).ready;
+}
+
 requestAnimationFrame(() => {
   requestAnimationFrame(() => {
-    if (window.testRunner)
-      testRunner.notifyDone();
+    waitForCompositor().then(() => {
+      if (window.testRunner)
+        testRunner.notifyDone();
+    });
   });
 });
 </script>