Unified Desktop: hook up ash to allow unified desktop mode

ash/host/ash_window_tree_host_ozone.cc

Index: ash/host/ash_window_tree_host_ozone.cc
diff --git a/ash/host/ash_window_tree_host_ozone.cc b/ash/host/ash_window_tree_host_ozone.cc
index cb2ec66e33dc4e08f0b2924c5a14473b2c71dac1..5cde3d481c32955ee3dab15c92e62c657f5a5742 100644
--- a/ash/host/ash_window_tree_host_ozone.cc
+++ b/ash/host/ash_window_tree_host_ozone.cc
@@ -5,6 +5,7 @@
 #include "ash/host/ash_window_tree_host.h"
 
 #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 "ash/host/transformer_helper.h"
 #include "base/command_line.h"
@@ -144,6 +145,8 @@ void AshWindowTreeHostOzone::SetTapToClickPaused(bool state) {
 
 AshWindowTreeHost* AshWindowTreeHost::Create(
     const AshWindowTreeHostInitParams& init_params) {
+  if (init_params.offscreen)
+    return new AshWindowTreeHostVirtual(init_params.initial_bounds);
   return new AshWindowTreeHostOzone(init_params.initial_bounds);
 }