[Android]Optimization of scrollbar animation.

cc/layers/scrollbar_layer_impl_base.h

Index: cc/layers/scrollbar_layer_impl_base.h
diff --git a/cc/layers/scrollbar_layer_impl_base.h b/cc/layers/scrollbar_layer_impl_base.h
index 435943dfc4ce28bd1a555101faa27a0ff00f2888..dd75b2dd5253ce3467374f27f9806bd500f19df2 100644
--- a/cc/layers/scrollbar_layer_impl_base.h
+++ b/cc/layers/scrollbar_layer_impl_base.h
@@ -54,6 +54,10 @@ class CC_EXPORT ScrollbarLayerImplBase : public LayerImpl {
   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();
@@ -98,6 +102,8 @@ class CC_EXPORT ScrollbarLayerImplBase : public LayerImpl {
 
   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);
 };