Add additive animation support for CSS property clip

third_party/WebKit/Source/core/animation/animatable/AnimatableLengthBox.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 24 matching lines @@
 PassRefPtr<AnimatableValue> AnimatableLengthBox::interpolateTo(const AnimatableValue* value, double fraction) const
 {
     const AnimatableLengthBox* lengthBox = toAnimatableLengthBox(value);
     return AnimatableLengthBox::create(
         AnimatableValue::interpolate(this->left(), lengthBox->left(), fraction),
         AnimatableValue::interpolate(this->right(), lengthBox->right(), fraction),
         AnimatableValue::interpolate(this->top(), lengthBox->top(), fraction),
         AnimatableValue::interpolate(this->bottom(), lengthBox->bottom(), fraction));
 }
 
+bool AnimatableLengthBox::usesDefaultInterpolationWith(const AnimatableValue* other) const
+{
+    const AnimatableLengthBox& otherBox = toAnimatableLengthBox(*other);
+    return usesDefaultInterpolation(left(), otherBox.left())
+        || usesDefaultInterpolation(right(), otherBox.right())
+        || usesDefaultInterpolation(top(), otherBox.top())
+        || usesDefaultInterpolation(bottom(), otherBox.bottom());
+}
+
 bool AnimatableLengthBox::equalTo(const AnimatableValue* value) const
 {
     const AnimatableLengthBox* lengthBox = toAnimatableLengthBox(value);
     return left()->equals(lengthBox->left())
         && right()->equals(lengthBox->right())
         && top()->equals(lengthBox->top())
         && bottom()->equals(lengthBox->bottom());
 }
 
 } // namespace blink