Route Scroll events through a cc::InputHandler

ui/compositor/layer.h

Index: ui/compositor/layer.h
diff --git a/ui/compositor/layer.h b/ui/compositor/layer.h
index 4bb77d315bdc7e96014a88a6b7a7e7e874c27ae5..a338ec2cc0e23c491f14692f76891bb982bf470c 100644
--- a/ui/compositor/layer.h
+++ b/ui/compositor/layer.h
@@ -355,6 +355,10 @@ class COMPOSITOR_EXPORT Layer
   // is invoked when scrolling performed by the cc::InputHandler is committed.
   void SetScrollable(Layer* parent_clip_layer, const base::Closure& on_scroll);
 
+  // Gets the ElementId. For a ui::Layer, this has primaryId equal to the
+  // LayerImpl's id() and a secondaryId of 0.
+  cc::ElementId GetElementId() const;
+
   // Gets and sets the current scroll offset of the layer.
   gfx::ScrollOffset CurrentScrollOffset() const;
   void SetScrollOffset(const gfx::ScrollOffset& offset);