Add support for setting TrackStart on solid color layers.

cc/layers/solid_color_scrollbar_layer.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_SOLID_COLOR_SCROLLBAR_LAYER_H_
 #define CC_LAYERS_SOLID_COLOR_SCROLLBAR_LAYER_H_
 
 #include "cc/base/cc_export.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/scrollbar_layer_interface.h"
 
 namespace cc {
 
 class CC_EXPORT SolidColorScrollbarLayer : public ScrollbarLayerInterface,
                                            public Layer {
  public:
   virtual scoped_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl)
       OVERRIDE;
 
   static scoped_refptr<SolidColorScrollbarLayer> Create(
       ScrollbarOrientation orientation,
       int thumb_thickness,
+      int track_start,
       bool is_left_side_vertical_scrollbar,
       int scroll_layer_id);
 
   // Layer overrides.
   virtual bool OpacityCanAnimateOnImplThread() const OVERRIDE;
   virtual ScrollbarLayerInterface* ToScrollbarLayer() OVERRIDE;
 
   virtual void PushPropertiesTo(LayerImpl* layer) OVERRIDE;
   virtual void PushScrollClipPropertiesTo(LayerImpl* layer) OVERRIDE;
 
   virtual void SetNeedsDisplayRect(const gfx::RectF&) OVERRIDE;
 
   // ScrollbarLayerInterface
   virtual int ScrollLayerId() const OVERRIDE;
   virtual void SetScrollLayer(int layer_id) OVERRIDE;
   virtual void SetClipLayer(int layer_id) OVERRIDE;
 
   virtual ScrollbarOrientation orientation() const OVERRIDE;
 
  protected:
   SolidColorScrollbarLayer(ScrollbarOrientation orientation,
                            int thumb_thickness,
+                           int track_start,
                            bool is_left_side_vertical_scrollbar,
                            int scroll_layer_id);
   virtual ~SolidColorScrollbarLayer();
 
  private:
   int scroll_layer_id_;
   int clip_layer_id_;
   ScrollbarOrientation orientation_;
   int thumb_thickness_;
+  int track_start_;
   bool is_left_side_vertical_scrollbar_;
 
   DISALLOW_COPY_AND_ASSIGN(SolidColorScrollbarLayer);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_SOLID_COLOR_SCROLLBAR_LAYER_H_