Web Animations: Correctly handle incomplete keyframes in CSS animations

Source/core/animation/KeyframeAnimationEffect.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 106 matching lines @@
 Keyframe::Keyframe()
     : m_offset(std::numeric_limits<double>::quiet_NaN())
     , m_composite(AnimationEffect::CompositeReplace)
 { }
 
 void Keyframe::setPropertyValue(CSSPropertyID property, const AnimatableValue* value)
 {
     m_propertyValues.add(property, const_cast<AnimatableValue*>(value));
 }
 
+void Keyframe::clearPropertyValue(CSSPropertyID property)
+{
+    m_propertyValues.remove(property);
+}
+
 const AnimatableValue* Keyframe::propertyValue(CSSPropertyID property) const
 {
     ASSERT(m_propertyValues.contains(property));
     return m_propertyValues.get(property);
 }
 
 PropertySet Keyframe::properties() const
 {
     // This is only used when setting up the keyframe groups, so there's no
     // need to cache the result.
@@ skipping 188 matching lines @@
 
     if ((*before)->offset() == offset)
         return const_cast<CompositableValue*>((*before)->value());
     if ((*after)->offset() == offset)
         return const_cast<CompositableValue*>((*after)->value());
     return BlendedCompositableValue::create((*before)->value(), (*after)->value(),
         (offset - (*before)->offset()) / ((*after)->offset() - (*before)->offset()));
 }
 
 } // namespace