Third part of porting Chrome Ash to Windows 7

ash/host/window_tree_host_factory.cc

 // 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.
 
 #include "ash/host/window_tree_host_factory.h"
 
 #include "ui/aura/window_tree_host.h"
 
 namespace {
 
 class WindowTreeHostFactoryImpl : public ash::WindowTreeHostFactory {
  public:
   WindowTreeHostFactoryImpl() {}
 
   // Overridden from WindowTreeHostFactory:
   virtual aura::WindowTreeHost* CreateWindowTreeHost(
       const gfx::Rect& initial_bounds) OVERRIDE {
     return aura::WindowTreeHost::Create(initial_bounds);
   }
 };
 
 }
 
 namespace ash {
-
+// static
+WindowTreeHostFactory* WindowTreeHostFactory::CreateForTest() {
+  return Create();
+}
 // static
 WindowTreeHostFactory* WindowTreeHostFactory::Create() {
   return new WindowTreeHostFactoryImpl;
 }
 
 }  // namespace ash