Introduce aura::Env controller to abstract away changes to aura::Env

ui/aura/window_event_dispatcher.h

 // Copyright 2014 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.
 
 #ifndef UI_AURA_WINDOW_EVENT_DISPATCHER_H_
 #define UI_AURA_WINDOW_EVENT_DISPATCHER_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 27 matching lines @@
 class GestureEvent;
 class GestureRecognizer;
 class KeyEvent;
 class MouseEvent;
 class ScrollEvent;
 class TouchEvent;
 }
 
 namespace aura {
 class TestScreen;
+class WindowEventDispatcherDelegate;
 class WindowTargeter;
 class WindowTreeHost;
 
 namespace test {
 class WindowEventDispatcherTestApi;
 }
 
 // WindowEventDispatcher orchestrates event dispatch within a window tree
 // owned by WindowTreeHost. WTH also owns the WED.
 // TODO(beng): In progress, remove functionality not directly related to
@@ skipping 207 matching lines @@
   // Allowing for reposting of events. Used when exiting context menus.
   std::unique_ptr<ui::LocatedEvent> held_repostable_event_;
 
   // Set when dispatching a held event.
   ui::LocatedEvent* dispatching_held_event_;
 
   ScopedObserver<aura::Window, aura::WindowObserver> observer_manager_;
 
   bool transform_events_;
 
+  std::unique_ptr<WindowEventDispatcherDelegate> delegate_;
+
   // Used to schedule reposting an event.
   base::WeakPtrFactory<WindowEventDispatcher> repost_event_factory_;
 
   // Used to schedule DispatchHeldEvents() when |move_hold_count_| goes to 0.
   base::WeakPtrFactory<WindowEventDispatcher> held_event_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowEventDispatcher);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_WINDOW_EVENT_DISPATCHER_H_