[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 36 matching lines @@
   virtual void PushPropertiesTo(LayerImpl* layer) OVERRIDE;
   virtual ScrollbarLayerImplBase* ToScrollbarLayer() OVERRIDE;
   void PushScrollClipPropertiesTo(LayerImpl* layer);
 
   void SetVisibleToTotalLengthRatio(float ratio);
   virtual gfx::Rect ComputeThumbQuadRect() const;
 
   float thumb_thickness_scale_factor() {
     return thumb_thickness_scale_factor_;
   }
+
+  void ResetScrollbarNeedsAnimation() { scrollbar_needs_animation_ = false; }
+  bool scrollbar_needs_animation() { return scrollbar_needs_animation_; }
+
   void SetThumbThicknessScaleFactor(float thumb_thickness_scale_factor);
 
   void ScrollbarParametersDidChange();
 
  protected:
   ScrollbarLayerImplBase(LayerTreeImpl* tree_impl,
                          int id,
                          ScrollbarOrientation orientation,
                          bool is_left_side_vertical_scrollbar,
                          bool is_overlay);
@@ skipping 24 matching lines @@
   int maximum_;
   ScrollbarOrientation orientation_;
   bool is_left_side_vertical_scrollbar_;
 
   // Difference between the clip layer's height and the visible viewport
   // height (which may differ in the presence of top-controls hiding).
   float vertical_adjust_;
 
   float visible_to_total_length_ratio_;
 
+  bool scrollbar_needs_animation_;

[aelias_OOO_until_Jul13, 2014/09/19 23:20:17]

I don't think it makes any sense to add a new boolean in this class because the
state is entirely transient and can be local to LayerImpl::SetScrollbarPosition
instead.  Please remove all the changes to this class and instead determine the
animatable boolean by comparing old values with new values within
LayerImpl::SetScrollbarPosition.

[danakj, 2014/09/19 23:25:56]

That's a good idea. Wei previously pointed out these Set methods already do an
== check, so we could make use of that by making them each return bool if they
changed something. Then LayerImpl can decide to animate if any of the functions
returns true.

[MuVen, 2014/09/20 08:42:00]

Yes this is good idea.This eliminates the needs for new bool and reseting the
bool. Thanks for the suggestions.

[MuVen, 2014/09/20 08:42:00]

Done.

+
   DISALLOW_COPY_AND_ASSIGN(ScrollbarLayerImplBase);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_SCROLLBAR_LAYER_IMPL_BASE_H_