Add mutableComponent() interface to InterpolationValue

Source/core/animation/PrimitiveInterpolation.h

 // Copyright 2015 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 PrimitiveInterpolation_h
 #define PrimitiveInterpolation_h
 
 #include "core/animation/InterpolationValue.h"
 #include "platform/animation/AnimationUtilities.h"
 #include "platform/heap/Handle.h"
@@ skipping 41 matching lines @@
         , m_start(start)
         , m_end(end)
         , m_nonInterpolableValue(nonInterpolableValue)
     { }
 
     void interpolateValue(double fraction, OwnPtr<InterpolationValue>& result) const final
     {
         ASSERT(result);
         ASSERT(&result->type() == &m_type);
         ASSERT(result->nonInterpolableValue() == m_nonInterpolableValue.get());
-        m_start->interpolate(*m_end, fraction, result->interpolableValue());
+        m_start->interpolate(*m_end, fraction, *result->mutableComponent().interpolableValue);
     }
 
     double interpolateUnderlyingFraction(double start, double end, double fraction) const final { return blend(start, end, fraction); }
 
     const InterpolationType& m_type;
     OwnPtr<InterpolableValue> m_start;
     OwnPtr<InterpolableValue> m_end;
     RefPtrWillBePersistent<NonInterpolableValue> m_nonInterpolableValue;
 };
 
@@ skipping 29 matching lines @@
     bool isFlip() const final { return true; }
 
     OwnPtr<InterpolationValue> m_start;
     OwnPtr<InterpolationValue> m_end;
     mutable double m_lastFraction;
 };
 
 } // namespace blink
 
 #endif // PrimitiveInterpolation_h