WIP: Eliminate event.target() usage from TrayEventFilter

ash/pointer_watcher_delegate_aura.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/ash_export.h"
 #include "ash/pointer_watcher_delegate.h"
 #include "base/macros.h"
 #include "base/observer_list.h"
 #include "ui/events/event_handler.h"
 
 namespace gfx {
 class Point;
 }
 
 namespace ui {
 class LocatedEvent;
 }
 
+namespace views {
+class Widget;
+}
+
 namespace ash {
 
 // Support for PointerWatchers in non-mus ash, implemented with a pre-target
 // EventHandler on the Shell.
 class ASH_EXPORT PointerWatcherDelegateAura : public PointerWatcherDelegate,
                                               public ui::EventHandler {
  public:
   PointerWatcherDelegateAura();
   ~PointerWatcherDelegateAura() override;
 
   // PointerWatcherDelegate:
   void AddPointerWatcher(views::PointerWatcher* watcher) override;
   void RemovePointerWatcher(views::PointerWatcher* watcher) override;
 
   // ui::EventHandler:
   void OnMouseEvent(ui::MouseEvent* event) override;
   void OnTouchEvent(ui::TouchEvent* event) override;
 
  private:
+  views::Widget* GetTargetWidget(const ui::LocatedEvent& event) const;
   gfx::Point GetLocationInScreen(const ui::LocatedEvent& event) const;
 
   // Must be empty on destruction.
   base::ObserverList<views::PointerWatcher, true> pointer_watchers_;
 
   DISALLOW_COPY_AND_ASSIGN(PointerWatcherDelegateAura);
 };
 
 }  // namespace ash