Route Scroll events through a cc::InputHandler

ui/compositor/compositor.h

Index: ui/compositor/compositor.h
diff --git a/ui/compositor/compositor.h b/ui/compositor/compositor.h
index 76f8f38765127232647b1fd02031924eb7782e3b..f78c3cfc20d4ab99db9c29777fa695b9e613f4d4 100644
--- a/ui/compositor/compositor.h
+++ b/ui/compositor/compositor.h
@@ -65,6 +65,7 @@ class CompositorVSyncManager;
 class LatencyInfo;
 class Layer;
 class Reflector;
+class UIScrollInputManager;
 
 #if defined(USE_AURA)
 class Window;
@@ -379,6 +380,10 @@ class COMPOSITOR_EXPORT Compositor
 
   const cc::FrameSinkId& frame_sink_id() const { return frame_sink_id_; }
 
+  UIScrollInputManager* scroll_input_manager() {
+    return scroll_input_manager_.get();
+  }
+
  private:
   friend class base::RefCounted<Compositor>;
   friend class CompositorLock;
@@ -427,6 +432,7 @@ class COMPOSITOR_EXPORT Compositor
   scoped_refptr<cc::AnimationTimeline> animation_timeline_;
 
   gfx::ColorSpace color_space_;
+  std::unique_ptr<UIScrollInputManager> scroll_input_manager_;
 
   base::WeakPtrFactory<Compositor> weak_ptr_factory_;