Convert scroll offsets to use SyncedProperty.

cc/animation/layer_animation_value_provider.h

 // Copyright 2013 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 CC_ANIMATION_LAYER_ANIMATION_VALUE_PROVIDER_H_
 #define CC_ANIMATION_LAYER_ANIMATION_VALUE_PROVIDER_H_
 
 #include "cc/base/cc_export.h"
 
 namespace gfx {
 class ScrollOffset;
 }
 
 namespace cc {
 
 // A LayerAnimationValueProvider is used for determining the starting value
 // for animations that start at their 'current' value rather than at a
 // pre-specified value.
 class CC_EXPORT LayerAnimationValueProvider {
  public:
   virtual ~LayerAnimationValueProvider() {}
 
-  virtual gfx::ScrollOffset ScrollOffsetForAnimation() const = 0;
+  virtual gfx::ScrollOffset ScrollOffsetForAnimation() = 0;
 };
 
 }  // namespace cc
 
 #endif  // CC_ANIMATION_LAYER_ANIMATION_VALUE_PROVIDER_H_