Add support for setting TrackStart on solid color layers.

cc/layers/solid_color_scrollbar_layer.cc

Index: cc/layers/solid_color_scrollbar_layer.cc
diff --git a/cc/layers/solid_color_scrollbar_layer.cc b/cc/layers/solid_color_scrollbar_layer.cc
index 4a8e7224989b92c41bb852bb025988305477a94f..8749398aa6897458753eb641484994b654504645 100644
--- a/cc/layers/solid_color_scrollbar_layer.cc
+++ b/cc/layers/solid_color_scrollbar_layer.cc
@@ -17,6 +17,7 @@ scoped_ptr<LayerImpl> SolidColorScrollbarLayer::CreateLayerImpl(
                                               id(),
                                               orientation(),
                                               thumb_thickness_,
+                                              track_start_,
                                               is_left_side_vertical_scrollbar_,
                                               kIsOverlayScrollbar)
       .PassAs<LayerImpl>();
@@ -25,24 +26,28 @@ scoped_ptr<LayerImpl> SolidColorScrollbarLayer::CreateLayerImpl(
 scoped_refptr<SolidColorScrollbarLayer> SolidColorScrollbarLayer::Create(
     ScrollbarOrientation orientation,
     int thumb_thickness,
+    int track_start,
     bool is_left_side_vertical_scrollbar,
     int scroll_layer_id) {
-  return make_scoped_refptr(new SolidColorScrollbarLayer(
-      orientation,
-      thumb_thickness,
-      is_left_side_vertical_scrollbar,
-      scroll_layer_id));
+  return make_scoped_refptr(
+      new SolidColorScrollbarLayer(orientation,
+                                   thumb_thickness,
+                                   track_start,
+                                   is_left_side_vertical_scrollbar,
+                                   scroll_layer_id));
 }
 
 SolidColorScrollbarLayer::SolidColorScrollbarLayer(
     ScrollbarOrientation orientation,
     int thumb_thickness,
+    int track_start,
     bool is_left_side_vertical_scrollbar,
     int scroll_layer_id)
     : scroll_layer_id_(Layer::INVALID_ID),
       clip_layer_id_(scroll_layer_id),
       orientation_(orientation),
       thumb_thickness_(thumb_thickness),
+      track_start_(track_start),
       is_left_side_vertical_scrollbar_(is_left_side_vertical_scrollbar) {}
 
 SolidColorScrollbarLayer::~SolidColorScrollbarLayer() {}