ozone: Initialize a subsystem only if necessary.

ui/gfx/ozone/surface_factory_ozone.cc

 // 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.
 
 #include "ui/gfx/ozone/surface_factory_ozone.h"
 
 #include <stdlib.h>
 
 #include "base/command_line.h"
 #include "ui/gfx/ozone/surface_ozone_canvas.h"
 #include "ui/gfx/ozone/surface_ozone_egl.h"
 
 namespace gfx {
 
 // static
 SurfaceFactoryOzone* SurfaceFactoryOzone::impl_ = NULL;
 
 SurfaceFactoryOzone::SurfaceFactoryOzone() {
+  CHECK(!impl_) << "There should only be a single SurfaceFactoryOzone.";
+  impl_ = this;
 }
 
 SurfaceFactoryOzone::~SurfaceFactoryOzone() {
+  CHECK_EQ(impl_, this);
+  impl_ = NULL;
 }
 
 SurfaceFactoryOzone* SurfaceFactoryOzone::GetInstance() {
   CHECK(impl_) << "No SurfaceFactoryOzone implementation set.";
   return impl_;
 }
 
-void SurfaceFactoryOzone::SetInstance(SurfaceFactoryOzone* impl) {
-  impl_ = impl;
-}
-
 intptr_t SurfaceFactoryOzone::GetNativeDisplay() {
   return 0;
 }
 
 scoped_ptr<SurfaceOzoneEGL> SurfaceFactoryOzone::CreateEGLSurfaceForWidget(
       gfx::AcceleratedWidget widget) {
   NOTIMPLEMENTED();
   return scoped_ptr<SurfaceOzoneEGL>();
 }
 
@@ skipping 24 matching lines @@
   NOTREACHED();
 }
 
 gfx::NativeBufferOzone SurfaceFactoryOzone::CreateNativeBuffer(
     gfx::Size size,
     BufferFormat format) {
   return 0;
 }
 
 }  // namespace gfx