Note scrollbar layer properties changed when position changes.

cc/layers/scrollbar_layer_impl.cc

 // Copyright 2012 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.
 
 #include "cc/layers/scrollbar_layer_impl.h"
 
 #include <algorithm>
 
 #include "cc/animation/scrollbar_animation_controller.h"
 #include "cc/layers/layer.h"
@@ skipping 152 matching lines @@
 gfx::Rect ScrollbarLayerImpl::ScrollbarLayerRectToContentRect(
     gfx::RectF layer_rect) const {
   // Don't intersect with the bounds as in layerRectToContentRect() because
   // layer_rect here might be in coordinates of the containing layer.
   gfx::RectF content_rect = gfx::ScaleRect(layer_rect,
                                            contents_scale_x(),
                                            contents_scale_y());
   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
   // horizontal scrollbar - inputs are above the scrollbar, computed values
   // below:
   //
   //    |<------------------- track_length_ ------------------->|
   //
   // |--| <-- start_offset
   //
@@ skipping 81 matching lines @@
 void ScrollbarLayerImpl::DidLoseOutputSurface() {
   track_resource_id_ = 0;
   thumb_resource_id_ = 0;
 }
 
 const char* ScrollbarLayerImpl::LayerTypeAsString() const {
   return "cc::ScrollbarLayerImpl";
 }
 
 }  // namespace cc