Delete unused AnimatableValue code

third_party/WebKit/Source/core/animation/animatable/AnimatableValue.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 12 matching lines @@
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "core/animation/animatable/AnimatableValue.h"
 
-#include "core/animation/animatable/AnimatableNeutral.h"
 #include "wtf/StdLibExtras.h"
 #include <algorithm>
 
 namespace blink {
 
-PassRefPtr<AnimatableValue> AnimatableValue::neutralValue() {
-  DEFINE_STATIC_REF(AnimatableNeutral, neutralSentinelValue,
-                    (AnimatableNeutral::create()));
-  return neutralSentinelValue;
-}
-
 PassRefPtr<AnimatableValue> AnimatableValue::interpolate(
     const AnimatableValue* left,
     const AnimatableValue* right,
     double fraction) {
   DCHECK(left);
   DCHECK(right);
-  DCHECK(!left->isNeutral());
-  DCHECK(!right->isNeutral());
 
   if (fraction && fraction != 1 && left->isSameType(right))
     return left->interpolateTo(right, fraction);
 
   return defaultInterpolateTo(left, right, fraction);
 }
 
 }  // namespace blink