Unified Desktop: hook up ash to allow unified desktop mode

ash/host/ash_window_tree_host_ozone.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/host/ash_window_tree_host_init_params.h"
+#include "ash/host/ash_window_tree_host_unified.h"
 #include "ash/host/root_window_transformer.h"
 #include "ash/host/transformer_helper.h"
 #include "base/command_line.h"
 #include "base/trace_event/trace_event.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_tree_host_ozone.h"
 #include "ui/events/null_event_targeter.h"
 #include "ui/gfx/geometry/insets.h"
 #include "ui/gfx/transform.h"
 #include "ui/ozone/public/input_controller.h"
@@ skipping 119 matching lines @@
   // Temporarily pause tap-to-click when the cursor is hidden.
   ui::OzonePlatform::GetInstance()->GetInputController()->SetTapToClickPaused(
       state);
 #endif
 }
 
 }  // namespace
 
 AshWindowTreeHost* AshWindowTreeHost::Create(
     const AshWindowTreeHostInitParams& init_params) {
+  if (init_params.offscreen)
+    return new AshWindowTreeHostUnified(init_params.initial_bounds);
   return new AshWindowTreeHostOzone(init_params.initial_bounds);
 }
 
 }  // namespace ash