Implement --ozone-platform flag to select OzonePlatform implementation at runtime

ui/ozone/platform/dri/ozone_platform_dri.cc

 // Copyright 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/ozone/platform/dri/ozone_platform_dri.h"
 
 #include "ui/ozone/ozone_platform.h"
 
 namespace ui {
 
 OzonePlatformDri::OzonePlatformDri() {}
 
 OzonePlatformDri::~OzonePlatformDri() {}
 
 gfx::SurfaceFactoryOzone* OzonePlatformDri::GetSurfaceFactoryOzone() {
   return &surface_factory_ozone_;
 }
 
 ui::EventFactoryOzone* OzonePlatformDri::GetEventFactoryOzone() {
   return &event_factory_ozone_;
 }
 
-OzonePlatform* CreateDefaultOzonePlatform() { return new OzonePlatformDri; }
+OzonePlatform* CreateOzonePlatformDri() { return new OzonePlatformDri; }
 
 }  // namespace ui