[WIP] Web Animations API: Constructing an Animation from partial keyframes throws a JS exception

Source/core/animation/KeyframeEffectModel.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 250 matching lines @@
         }
     }
 
     // Add synthetic keyframes.
     for (KeyframeGroupMap::iterator iter = m_keyframeGroups->begin(); iter != m_keyframeGroups->end(); ++iter) {
         iter->value->addSyntheticKeyframeIfRequired();
         iter->value->removeRedundantKeyframes();
     }
 }
 
+bool KeyframeEffectModel::isReplaceOnly()
+{
+    ensureKeyframeGroups();
+    for (KeyframeGroupMap::iterator iter = m_keyframeGroups->begin(); iter != m_keyframeGroups->end(); ++iter) {
+        const PropertySpecificKeyframeVector& keyframeVector = iter->value->keyframes();
+        for (size_t i = 0; i < keyframeVector.size(); ++i) {
+            if (keyframeVector[i]->value()->dependsOnUnderlyingValue()) {
+                return false;
+            }
+        }
+    }
+    return true;
+}
 
 KeyframeEffectModel::PropertySpecificKeyframe::PropertySpecificKeyframe(double offset, PassRefPtr<TimingFunction> easing, const AnimatableValue* value, CompositeOperation composite)
     : m_offset(offset)
     , m_easing(easing)
     , m_value(composite == AnimationEffect::CompositeReplace ?
         AnimatableValue::takeConstRef(value) :
         static_cast<PassRefPtr<CompositableValue> >(AddCompositableValue::create(value)))
 {
 }
 
@@ skipping 107 matching lines @@
         fraction = timingFunction->evaluate(fraction, accuracyForKeyframeEasing);
     return BlendedCompositableValue::create((*before)->value(), (*after)->value(), fraction);
 }
 
 void KeyframeEffectModel::trace(Visitor* visitor)
 {
     visitor->trace(m_keyframes);
 }
 
 } // namespace