Web Animations: Remove confusing interpolation subdirectory.

Source/core/animation/StyleInterpolation.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef StyleInterpolation_h
 #define StyleInterpolation_h
 
 #include "core/CSSPropertyNames.h"
-#include "core/animation/interpolation/Interpolation.h"
+#include "core/animation/Interpolation.h"
 
 namespace blink {
 
 class StyleResolverState;
 
 class StyleInterpolation : public Interpolation {
 public:
     // 1) convert m_cachedValue into an X
     // 2) shove X into StyleResolverState
     // X can be:
@@ skipping 19 matching lines @@
         , m_id(id)
     {
     }
 };
 
 DEFINE_TYPE_CASTS(StyleInterpolation, Interpolation, value, value->isStyleInterpolation(), value.isStyleInterpolation());
 
 }
 
 #endif