Add support for setting TrackStart on solid color layers.

webkit/renderer/compositor_bindings/web_compositor_support_impl.cc

Index: webkit/renderer/compositor_bindings/web_compositor_support_impl.cc
diff --git a/webkit/renderer/compositor_bindings/web_compositor_support_impl.cc b/webkit/renderer/compositor_bindings/web_compositor_support_impl.cc
index fe6c1f2c2f2fffb10d438aa1d19753ce597f64ca..09af014a874727788bdc4e45d51554e584f66001 100644
--- a/webkit/renderer/compositor_bindings/web_compositor_support_impl.cc
+++ b/webkit/renderer/compositor_bindings/web_compositor_support_impl.cc
@@ -87,10 +87,22 @@ WebScrollbarLayer* WebCompositorSupportImpl::createScrollbarLayer(
 }
 
 WebScrollbarLayer* WebCompositorSupportImpl::createSolidColorScrollbarLayer(
-      WebScrollbar::Orientation orientation, int thumb_thickness,
-      bool is_left_side_vertical_scrollbar) {
-  return new WebScrollbarLayerImpl(orientation, thumb_thickness,
-      is_left_side_vertical_scrollbar);
+    WebScrollbar::Orientation orientation,
+    int thumb_thickness,
+    int track_start,
+    bool is_left_side_vertical_scrollbar) {
+  return new WebScrollbarLayerImpl(orientation,
+                                   thumb_thickness,
+                                   track_start,
+                                   is_left_side_vertical_scrollbar);
+}
+
+WebScrollbarLayer* WebCompositorSupportImpl::createSolidColorScrollbarLayer(
+    WebScrollbar::Orientation orientation,
+    int thumb_thickness,
+    bool is_left_side_vertical_scrollbar) {
+  return new WebScrollbarLayerImpl(
+      orientation, thumb_thickness, 0, is_left_side_vertical_scrollbar);
 }
 
 WebAnimation* WebCompositorSupportImpl::createAnimation(