events: Move the PlatformEventSource creation in aura::Env.

ui/aura/env.h

 // Copyright (c) 2012 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_ENV_H_
 #define UI_AURA_ENV_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
 #include "ui/aura/aura_export.h"
 #include "ui/events/event_handler.h"
 #include "ui/events/event_target.h"
 #include "ui/gfx/point.h"
 
+namespace ui {
+class PlatformEventSource;
+}
 namespace aura {
 
 namespace test {
 class EnvTestHelper;
 }
 
 class EnvObserver;
 class InputStateLookup;
 class Window;
 class WindowTreeHost;
@@ skipping 54 matching lines @@
 
   ObserverList<EnvObserver> observers_;
 
   static Env* instance_;
   int mouse_button_flags_;
   // Location of last mouse event, in screen coordinates.
   gfx::Point last_mouse_location_;
   bool is_touch_down_;
 
   scoped_ptr<InputStateLookup> input_state_lookup_;
+  scoped_ptr<ui::PlatformEventSource> event_source_;
 
   DISALLOW_COPY_AND_ASSIGN(Env);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_ENV_H_