[Android]Optimization of scrollbar animation.

cc/layers/scrollbar_layer_impl_base.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_LAYERS_SCROLLBAR_LAYER_IMPL_BASE_H_
 #define CC_LAYERS_SCROLLBAR_LAYER_IMPL_BASE_H_
 
 #include "cc/base/cc_export.h"
 #include "cc/input/scrollbar.h"
 #include "cc/layers/layer.h"
@@ skipping 40 matching lines @@
   void SetVisibleToTotalLengthRatio(float ratio);
   virtual gfx::Rect ComputeThumbQuadRect() const;
 
   float thumb_thickness_scale_factor() {
     return thumb_thickness_scale_factor_;
   }
   void SetThumbThicknessScaleFactor(float thumb_thickness_scale_factor);
 
   void ScrollbarParametersDidChange();
 
+  bool ScrollbarNeedsUpdate(float vertical_adjust,

[weiliangc, 2014/09/15 17:14:37]

The four setter function already checks whether the value has changed. I don't
think you need a new function for this.

+                            float current_pos,
+                            int maximum,
+                            float visible_to_total_length_ratio);
+
  protected:
   ScrollbarLayerImplBase(LayerTreeImpl* tree_impl,
                          int id,
                          ScrollbarOrientation orientation,
                          bool is_left_side_vertical_scrollbar,
                          bool is_overlay);
   virtual ~ScrollbarLayerImplBase();
 
   gfx::Rect ScrollbarLayerRectToContentRect(const gfx::RectF& layer_rect) const;
 
@@ skipping 26 matching lines @@
   float vertical_adjust_;
 
   float visible_to_total_length_ratio_;
 
   DISALLOW_COPY_AND_ASSIGN(ScrollbarLayerImplBase);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_SCROLLBAR_LAYER_IMPL_BASE_H_