Add ability to create solid color scrollbars in ScrollingCoordinator.

Source/core/page/scrolling/ScrollingCoordinator.h

Index: Source/core/page/scrolling/ScrollingCoordinator.h
diff --git a/Source/core/page/scrolling/ScrollingCoordinator.h b/Source/core/page/scrolling/ScrollingCoordinator.h
index 175c97d20175081e45ff399163b4a06eb2bea074..bdd92023456374e49a808465b7eee2b84fa99f74 100644
--- a/Source/core/page/scrolling/ScrollingCoordinator.h
+++ b/Source/core/page/scrolling/ScrollingCoordinator.h
@@ -90,6 +90,8 @@ public:
     MainThreadScrollingReasons mainThreadScrollingReasons() const;
     bool shouldUpdateScrollLayerPositionOnMainThread() const { return mainThreadScrollingReasons() != 0; }
 
+    PassOwnPtr<WebKit::WebScrollbarLayer> createSolidColorScrollbarLayer(ScrollbarOrientation, int thumbThickness);
+
     void willDestroyScrollableArea(ScrollableArea*);
     // Returns true if the coordinator handled this change.
     bool scrollableAreaScrollLayerDidChange(ScrollableArea*);