Unified Desktop: hook up ash to allow unified desktop mode

ash/host/ash_window_tree_host_x11.cc

Index: ash/host/ash_window_tree_host_x11.cc
diff --git a/ash/host/ash_window_tree_host_x11.cc b/ash/host/ash_window_tree_host_x11.cc
index 882ef13409b01a0ddfaca88b6412efdec2f3bc5e..976cdfad201965cc2656a196ee64194bee29fd12 100644
--- a/ash/host/ash_window_tree_host_x11.cc
+++ b/ash/host/ash_window_tree_host_x11.cc
@@ -13,6 +13,7 @@
 #include <vector>
 
 #include "ash/host/ash_window_tree_host_init_params.h"
+#include "ash/host/ash_window_tree_host_virtual.h"
 #include "ash/host/root_window_transformer.h"
 #include "base/basictypes.h"
 #include "base/sys_info.h"
@@ -280,6 +281,8 @@ void AshWindowTreeHostX11::SetCrOSTapPaused(bool state) {
 
 AshWindowTreeHost* AshWindowTreeHost::Create(
     const AshWindowTreeHostInitParams& init_params) {
+  if (init_params.offscreen)
+    return new AshWindowTreeHostVirtual(init_params.initial_bounds);
   return new AshWindowTreeHostX11(init_params.initial_bounds);
 }