WIP: Eliminate event.target() usage from TrayEventFilter

ash/shelf/overflow_bubble.h

Index: ash/shelf/overflow_bubble.h
diff --git a/ash/shelf/overflow_bubble.h b/ash/shelf/overflow_bubble.h
index 0a9985a6b5257cfcb6d7151155790d7193f8df3f..14d1450084c289b7790ed45b2427f6382bb21314 100644
--- a/ash/shelf/overflow_bubble.h
+++ b/ash/shelf/overflow_bubble.h
@@ -47,9 +47,11 @@ class OverflowBubble : public views::PointerWatcher,
 
   // views::PointerWatcher:
   void OnMousePressed(const ui::MouseEvent& event,
-                      const gfx::Point& location_in_screen) override;
+                      const gfx::Point& location_in_screen,
+                      views::Widget* target) override;
   void OnTouchPressed(const ui::TouchEvent& event,
-                      const gfx::Point& location_in_screen) override;
+                      const gfx::Point& location_in_screen,
+                      views::Widget* target) override;
 
   // Overridden from views::WidgetObserver:
   void OnWidgetDestroying(views::Widget* widget) override;