Revert of Remove remote tree host and some related input and metro_driver code

ash/host/ash_window_tree_host_win.cc

 // 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.
 
 #include "ash/host/ash_window_tree_host.h"
 
 #include "ash/ash_export.h"
 #include "ash/ash_switches.h"
+#include "ash/host/ash_remote_window_tree_host_win.h"
 #include "ash/host/ash_window_tree_host_init_params.h"
 #include "ash/host/root_window_transformer.h"
 #include "ash/host/transformer_helper.h"
 #include "ash/ime/input_method_event_handler.h"
 #include "base/command_line.h"
 #include "base/win/windows_version.h"
 #include "ui/aura/window_tree_host_platform.h"
 #include "ui/events/event_processor.h"
 #include "ui/gfx/geometry/insets.h"
 #include "ui/gfx/transform.h"
@@ skipping 96 matching lines @@
 
   TransformerHelper transformer_helper_;
 
   DISALLOW_COPY_AND_ASSIGN(AshWindowTreeHostWin);
 };
 
 }  // namespace
 
 AshWindowTreeHost* AshWindowTreeHost::Create(
     const AshWindowTreeHostInitParams& init_params) {
+  if (base::win::GetVersion() >= base::win::VERSION_WIN7 &&
+      !base::CommandLine::ForCurrentProcess()->HasSwitch(
+          ash::switches::kForceAshToDesktop))
+    return new AshRemoteWindowTreeHostWin(init_params.remote_hwnd);
+
   return new AshWindowTreeHostWin(init_params.initial_bounds);
 }
 
 }  // namespace ash