Web Animations API: Constructing an Animation from a partial keyframe throws a JS exception

Source/core/animation/KeyframeEffectModel.cpp

Index: Source/core/animation/KeyframeEffectModel.cpp
diff --git a/Source/core/animation/KeyframeEffectModel.cpp b/Source/core/animation/KeyframeEffectModel.cpp
index 860452c01879ecefb52197031b3a2f187d688745..a5e7eea045902062da620e5c9c2115da2534efd1 100644
--- a/Source/core/animation/KeyframeEffectModel.cpp
+++ b/Source/core/animation/KeyframeEffectModel.cpp
@@ -244,24 +244,39 @@ void KeyframeEffectModel::ensureInterpolationEffect() const
     }
 }
 
+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]->composite() != AnimationEffect::CompositeReplace)
+                return false;
+        }
+    }
+    return true;
+}
+
 KeyframeEffectModel::PropertySpecificKeyframe::PropertySpecificKeyframe(double offset, PassRefPtr<TimingFunction> easing, const AnimatableValue* value, CompositeOperation composite)
     : m_offset(offset)
     , m_easing(easing)
+    , m_composite(composite)
 {
     m_value = AnimatableValue::takeConstRef(value);
 }
 
-KeyframeEffectModel::PropertySpecificKeyframe::PropertySpecificKeyframe(double offset, PassRefPtr<TimingFunction> easing, PassRefPtr<AnimatableValue> value)
+KeyframeEffectModel::PropertySpecificKeyframe::PropertySpecificKeyframe(double offset, PassRefPtr<TimingFunction> easing, PassRefPtr<AnimatableValue> value, CompositeOperation composite)
     : m_offset(offset)
     , m_easing(easing)
     , m_value(value)
+    , m_composite(composite)
 {
     ASSERT(!isNull(m_offset));
 }
 
 PassOwnPtr<KeyframeEffectModel::PropertySpecificKeyframe> KeyframeEffectModel::PropertySpecificKeyframe::cloneWithOffset(double offset) const
 {
-    return adoptPtr(new PropertySpecificKeyframe(offset, m_easing, m_value));
+    return adoptPtr(new PropertySpecificKeyframe(offset, m_easing, m_value, m_composite));
 }