Add support for new scroll valuators coming from CMT

ui/aura/root_window.h

Index: ui/aura/root_window.h
diff --git a/ui/aura/root_window.h b/ui/aura/root_window.h
index 52640dc4988dfb4afad2f95f625a89361982aec4..d59895596491abd56d83bc7e28de37cd22c83e22 100644
--- a/ui/aura/root_window.h
+++ b/ui/aura/root_window.h
@@ -38,6 +38,7 @@ class KeyEvent;
 class MouseEvent;
 class ScreenAura;
 class StackingClient;
+class ScrollEvent;
 class TouchEvent;
 
 // RootWindow is responsible for hosting a set of windows.
@@ -85,6 +86,9 @@ class AURA_EXPORT RootWindow : public ui::CompositorDelegate,
   // Handles a key event. Returns true if handled.
   bool DispatchKeyEvent(KeyEvent* event);
 
+  // Handles a scroll event. Returns true if handled.
+  bool DispatchScrollEvent(ScrollEvent* event);
+
   // Handles a touch event. Returns true if handled.
   bool DispatchTouchEvent(TouchEvent* event);