ozone: Initialize a subsystem only if necessary.

ui/base/cursor/ozone/cursor_factory_ozone.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_BASE_CURSOR_OZONE_CURSOR_FACTORY_OZONE_H_
 #define UI_BASE_CURSOR_OZONE_CURSOR_FACTORY_OZONE_H_
 
 #include "ui/base/cursor/cursor.h"
 #include "ui/base/ui_base_export.h"
 #include "ui/gfx/native_widget_types.h"
 
 namespace ui {
 
 class UI_BASE_EXPORT CursorFactoryOzone {
  public:
   CursorFactoryOzone();
   virtual ~CursorFactoryOzone();
 
-  // Returns the static instance.
+  // Returns the singleton instance.
   static CursorFactoryOzone* GetInstance();
 
-  // Sets the static instance. Ownership is retained by the caller.
-  static void SetInstance(CursorFactoryOzone* impl);
-
   // Return the default cursor of the specified type. The types are listed in
   // ui/base/cursor/cursor.h. Default cursors are managed by the implementation
   // and must live indefinitely; there's no way to know when to free them.
   virtual PlatformCursor GetDefaultCursor(int type);
 
   // Return a image cursor from the specified image & hotspot. Image cursors
   // are referenced counted and have an initial refcount of 1. Therefore, each
   // CreateImageCursor call must be matched with a call to UnrefImageCursor.
   virtual PlatformCursor CreateImageCursor(const SkBitmap& bitmap,
                                            const gfx::Point& hotspot);
@@ skipping 13 matching lines @@
   // WindowTreeHost::CanDispatchEvent() is no longer present.
   virtual gfx::AcceleratedWidget GetCursorWindow();
 
  private:
   static CursorFactoryOzone* impl_;  // not owned
 };
 
 }  // namespace gfx
 
 #endif  // UI_BASE_CURSOR_OZONE_CURSOR_FACTORY_OZONE_H_