Add switch to run ash tests on desktop in windows 8.

ash/host/root_window_host_factory_win.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/root_window_host_factory.h"
 
+#include "ash/ash_switches.h"
+#include "base/command_line.h"
 #include "base/win/windows_version.h"
 #include "ui/aura/remote_root_window_host_win.h"
 #include "ui/aura/root_window_host.h"
 
 namespace {
 
 class RootWindowHostFactoryImpl : public ash::RootWindowHostFactory {
  public:
   RootWindowHostFactoryImpl() {}
 
   // Overridden from RootWindowHostFactory:
   virtual aura::RootWindowHost* CreateRootWindowHost(
       const gfx::Rect& initial_bounds) OVERRIDE {
-    if (base::win::GetVersion() >= base::win::VERSION_WIN8)
+    if (base::win::GetVersion() >= base::win::VERSION_WIN8 &&
+        !CommandLine::ForCurrentProcess()->HasSwitch(
+            ash::switches::kForceAshToDesktop))
       return aura::RemoteRootWindowHostWin::Create(initial_bounds);
 
     return aura::RootWindowHost::Create(initial_bounds);
   }
 };
 
 }
 
 namespace ash {
 
 // static
 RootWindowHostFactory* RootWindowHostFactory::Create() {
   return new RootWindowHostFactoryImpl;
 }
 
 }  // namespace ash