ozone: Initialize a subsystem only if necessary.

ui/events/ozone/event_factory_ozone.h

 // Copyright (c) 2013 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_EVENTS_OZONE_EVENT_FACTORY_OZONE_H_
 #define UI_EVENTS_OZONE_EVENT_FACTORY_OZONE_H_
 
 #include <map>
 
 #include "base/memory/scoped_ptr.h"
@@ skipping 26 matching lines @@
   // an EventFactoryOzone but not all of them should process events. In chrome,
   // events are dispatched in the browser process on the UI thread.
   virtual void StartProcessingEvents();
 
   // Request to warp the cursor to a location within an AccelerateWidget.
   // If the cursor actually moves, the implementation must dispatch a mouse
   // move event with the new location.
   virtual void WarpCursorTo(gfx::AcceleratedWidget widget,
                             const gfx::PointF& location);
 
-  // Returns the static instance last set using SetInstance().
+  // Returns the singleton instance.
   static EventFactoryOzone* GetInstance();
 
-  // Sets the implementation delegate. Ownership is retained by the caller.
-  static void SetInstance(EventFactoryOzone*);
-
  private:
   static EventFactoryOzone* impl_;  // not owned
 
   DISALLOW_COPY_AND_ASSIGN(EventFactoryOzone);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_OZONE_EVENT_FACTORY_OZONE_H_