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 54 matching lines @@
     ASSERT(values.isEmpty());
 
     for (const auto& keyframe : effect->getPropertySpecificKeyframes(id)) {
         double offset = keyframe->offset() * scale;
         values.append(keyframe->cloneWithOffset(offset));
     }
 }
 
 }
 
+CSSPropertyID CompositorAnimations::CompositableProperties[3] = {
+    CSSPropertyOpacity, CSSPropertyTransform, CSSPropertyWebkitFilter
+};
+
 bool CompositorAnimations::getAnimatedBoundingBox(FloatBox& box, const AnimationEffect& effect, double minValue, double maxValue) const
 {
     const KeyframeEffectModelBase& keyframeEffect = toKeyframeEffectModelBase(effect);
 
     PropertySet properties = keyframeEffect.properties();
 
     if (properties.isEmpty())
         return true;
 
     minValue = std::min(minValue, 0.0);
@@ skipping 55 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())

[dstockwell, 2015/02/05 23:04:52]

When can getAnimatableValue() return null here?

[shend, 2015/02/06 03:16:25]

Since we're using StringKeyframes, initially the animatable values for all the
keyframes are null. For performance, we only snapshot animatable values for
compositable properties. So any keyframe that has non-compositable properties
will have a null animatable value (with the exception of keyframes using
LegacyStyleInterpolation). 

                 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