Remove --ash-enable-tray-dragging flag

ash/wm/gestures/shelf_gesture_handler.h

Index: ash/wm/gestures/shelf_gesture_handler.h
diff --git a/ash/wm/gestures/shelf_gesture_handler.h b/ash/wm/gestures/shelf_gesture_handler.h
index 974bf2b1583ccf2a3d2e61bee30ba16c274cdd0a..c7211db11e9596b4e5c87a6c186cc729f8c64052 100644
--- a/ash/wm/gestures/shelf_gesture_handler.h
+++ b/ash/wm/gestures/shelf_gesture_handler.h
@@ -13,7 +13,6 @@ class GestureEvent;
 }
 
 namespace ash {
-class TrayGestureHandler;
 
 // This manages gestures on the shelf (e.g. launcher, status tray) that affects
 // the shelf visibility.
@@ -30,8 +29,6 @@ class ShelfGestureHandler {
  private:
   bool drag_in_progress_;
 
-  scoped_ptr<TrayGestureHandler> tray_handler_;
-
   DISALLOW_COPY_AND_ASSIGN(ShelfGestureHandler);
 };