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

ash/host/ash_window_tree_host_win.cc

Index: ash/host/ash_window_tree_host_win.cc
diff --git a/ash/host/ash_window_tree_host_win.cc b/ash/host/ash_window_tree_host_win.cc
index 98d6b104c9dd318c9463724628d3c93b46dd89ec..287fc56bc64b320c3b2bc06ac74ef168bd09ab82 100644
--- a/ash/host/ash_window_tree_host_win.cc
+++ b/ash/host/ash_window_tree_host_win.cc
@@ -6,6 +6,7 @@
 
 #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"
@@ -122,6 +123,11 @@
 
 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);
 }