[Android]Optimization of scrollbar animation.

cc/layers/scrollbar_layer_impl_base.cc

Index: cc/layers/scrollbar_layer_impl_base.cc
diff --git a/cc/layers/scrollbar_layer_impl_base.cc b/cc/layers/scrollbar_layer_impl_base.cc
index 62b7dee0ad9c297f99d22a4826cdaf498ac21d96..c66eb5e994e6dabb0b037d2d74b5f264d6601602 100644
--- a/cc/layers/scrollbar_layer_impl_base.cc
+++ b/cc/layers/scrollbar_layer_impl_base.cc
@@ -26,7 +26,9 @@ ScrollbarLayerImplBase::ScrollbarLayerImplBase(
       orientation_(orientation),
       is_left_side_vertical_scrollbar_(is_left_side_vertical_scrollbar),
       vertical_adjust_(0.f),
-      visible_to_total_length_ratio_(1.f) {}
+      visible_to_total_length_ratio_(1.f),
+      scrollbar_needs_animation_(false) {
+}
 
 ScrollbarLayerImplBase::~ScrollbarLayerImplBase() {}
 
@@ -109,6 +111,7 @@ void ScrollbarLayerImplBase::SetCurrentPos(float current_pos) {
   if (current_pos_ == current_pos)
     return;
   current_pos_ = current_pos;
+  scrollbar_needs_animation_ = true;
   NoteLayerPropertyChanged();
 }
 
@@ -116,6 +119,7 @@ void ScrollbarLayerImplBase::SetMaximum(int maximum) {
   if (maximum_ == maximum)
     return;
   maximum_ = maximum;
+  scrollbar_needs_animation_ = true;
   NoteLayerPropertyChanged();
 }
 
@@ -123,6 +127,7 @@ void ScrollbarLayerImplBase::SetVerticalAdjust(float vertical_adjust) {
   if (vertical_adjust_ == vertical_adjust)
     return;
   vertical_adjust_ = vertical_adjust;
+  scrollbar_needs_animation_ = true;
   NoteLayerPropertyChanged();
 }
 
@@ -133,6 +138,7 @@ void ScrollbarLayerImplBase::SetVisibleToTotalLengthRatio(float ratio) {
   if (visible_to_total_length_ratio_ == ratio)
     return;
   visible_to_total_length_ratio_ = ratio;
+  scrollbar_needs_animation_ = true;
   NoteLayerPropertyChanged();
 }
 
@@ -140,6 +146,7 @@ void ScrollbarLayerImplBase::SetThumbThicknessScaleFactor(float factor) {
   if (thumb_thickness_scale_factor_ == factor)
     return;
   thumb_thickness_scale_factor_ = factor;
+  scrollbar_needs_animation_ = true;
   NoteLayerPropertyChanged();
 }