Note scrollbar layer properties changed when position changes.

cc/layers/scrollbar_layer_impl.cc

Index: cc/layers/scrollbar_layer_impl.cc
diff --git a/cc/layers/scrollbar_layer_impl.cc b/cc/layers/scrollbar_layer_impl.cc
index 0dcfcdec74114860caf02f5064b3cc972d118ba5..fef5600f99f5c7b2bf23fe6e9565ec7277a3d725 100644
--- a/cc/layers/scrollbar_layer_impl.cc
+++ b/cc/layers/scrollbar_layer_impl.cc
@@ -170,6 +170,16 @@ gfx::Rect ScrollbarLayerImpl::ScrollbarLayerRectToContentRect(
   return gfx::ToEnclosingRect(content_rect);
 }
 
+void ScrollbarLayerImpl::SetCurrentPos(float current_pos) {
+  current_pos_ = current_pos;
+  NoteLayerPropertyChanged();
+}
+
+void ScrollbarLayerImpl::SetMaximum(int maximum) {
+  maximum_ = maximum;

[danakj, 2013/08/13 19:32:40]

Yes please early out here if maximum_ == maximum. Same for above.

+  NoteLayerPropertyChanged();
+}
+
 gfx::Rect ScrollbarLayerImpl::ComputeThumbQuadRect() const {
   // Thumb extent is the length of the thumb in the scrolling direction, thumb
   // thickness is in the perpendicular direction. Here's an example of a