Drop "only composite opacity animations when already in compositing mode".

LayoutTests/transitions/opacity-transition-zindex.html

Index: LayoutTests/transitions/opacity-transition-zindex.html
diff --git a/LayoutTests/transitions/opacity-transition-zindex.html b/LayoutTests/transitions/opacity-transition-zindex.html
index 4ce9fc2d4da6db53723c08372fdb1e99ddf99da8..c36bec3cda42b5d3ab51265aef93016db60f4c0f 100644
--- a/LayoutTests/transitions/opacity-transition-zindex.html
+++ b/LayoutTests/transitions/opacity-transition-zindex.html
@@ -47,12 +47,11 @@
       container.style.opacity = 1;
       
       // dump the tree in the middle of the transition
-      if (window.testRunner)
-        window.setTimeout(function() {
-          var firstElement = document.getElementById('first');
-          internals.pauseAnimations(2.5);
+      if (window.internals && window.testRunner) {

[dstockwell, 2013/12/03 18:49:30]

Please format this as:

if (window.internals) {
  internals...
}
if (window.testRunner) {
  testRunner...
}

This allows the test to function correctly under --expose-internals-for-testing
where internals is exposed but testRunner is not.

+          window.internals.forceCompositingUpdate(document);
+          window.internals.pauseAnimations(2.5);
           testRunner.notifyDone();
-        }, 0);
+      }
     }
     // FIXME: this should use runTransitionTest().
     window.addEventListener('load', runTest, false);