Prepare for responsive CSS animations.

Source/core/animation/CompositorAnimations.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 129 matching lines @@
     PropertySet properties = keyframeEffect.properties();
 
     if (properties.isEmpty())
         return false;
 
     for (const auto& property : properties) {
         const PropertySpecificKeyframeVector& keyframes = keyframeEffect.getPropertySpecificKeyframes(property);
         ASSERT(keyframes.size() >= 2);
         for (const auto& keyframe : keyframes) {
             // FIXME: Determine candidacy based on the CSSValue instead of a snapshot AnimatableValue.
-            if (keyframe->composite() != AnimationEffect::CompositeReplace || !keyframe->getAnimatableValue())
+            bool isNeutralKeyframe = keyframe->isStringPropertySpecificKeyframe() && !toStringPropertySpecificKeyframe(keyframe.get())->value() && keyframe->composite() == AnimationEffect::CompositeAdd;
+            if ((keyframe->composite() != AnimationEffect::CompositeReplace && !isNeutralKeyframe) || !keyframe->getAnimatableValue() || !isCompositableProperty(property))

[dstockwell, 2015/01/27 02:22:58]

I don't understand the isCompositableProperty test here, won't we already return
false on line 168?

[shend, 2015/01/28 02:44:50]

Done.

                 return false;
 
             switch (property) {
             case CSSPropertyOpacity:
                 break;
             case CSSPropertyTransform:
                 if (toAnimatableTransform(keyframe->getAnimatableValue().get())->transformOperations().dependsOnBoxSize())
                     return false;
                 break;
             case CSSPropertyWebkitFilter: {
@@ skipping 381 matching lines @@
             break;
         default:
             ASSERT_NOT_REACHED();
         }
         animations.append(animation.release());
     }
     ASSERT(!animations.isEmpty());
 }
 
 } // namespace blink