Set track_start on solid color layers to the margin.

public/platform/WebCompositorSupport.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 62 matching lines @@
     virtual WebImageLayer* createImageLayer() { return 0; }
 
     virtual WebNinePatchLayer* createNinePatchLayer() { return 0; }
 
     // TODO(dshwang): This isn't used anymore.
     virtual WebSolidColorLayer* createSolidColorLayer() { return 0; }
 
     // The ownership of the WebScrollbarThemeGeometry pointer is passed to Chromium.
     virtual WebScrollbarLayer* createScrollbarLayer(WebScrollbar*, WebScrollbarThemePainter, WebScrollbarThemeGeometry*) { return 0; }
 
-    virtual WebScrollbarLayer* createSolidColorScrollbarLayer(WebScrollbar::Orientation, int thumbThickness, bool isLeftSideVerticalScrollbar) { return 0; }
+    virtual WebScrollbarLayer* createSolidColorScrollbarLayer(WebScrollbar::Orientation, int thumbThickness, int trackStart, bool isLeftSideVerticalScrollbar) { return 0; }
 
     // Animation ----------------------------------------------------
 
     virtual WebAnimation* createAnimation(const WebAnimationCurve&, WebAnimation::TargetProperty, int animationId = 0) { return 0; }
 
     virtual WebFilterAnimationCurve* createFilterAnimationCurve() { return 0; }
 
     virtual WebFloatAnimationCurve* createFloatAnimationCurve() { return 0; }
 
     virtual WebTransformAnimationCurve* createTransformAnimationCurve() { return 0; }
 
     virtual WebTransformOperations* createTransformOperations() { return 0; }
 
     virtual WebFilterOperations* createFilterOperations() { return 0; }
 
 protected:
     virtual ~WebCompositorSupport() { }
 };
 
 }
 
 #endif // WebCompositorSupport_h