Makes RootWindowController window creation in terms of common types

ash/wm/aura/wm_globals_aura.cc

 // Copyright 2016 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/wm/aura/wm_globals_aura.h"
 
 #include "ash/display/window_tree_host_manager.h"
 #include "ash/session/session_state_delegate.h"
 #include "ash/shell.h"
 #include "ash/shell_delegate.h"
@@ skipping 22 matching lines @@
   if (added_activation_observer_) {
     aura::client::GetActivationClient(Shell::GetPrimaryRootWindow())
         ->RemoveObserver(this);
   }
   if (added_display_observer_)
     Shell::GetInstance()->window_tree_host_manager()->RemoveObserver(this);
 
   Shell::GetInstance()->RemoveShellObserver(this);
 }
 
+WmWindow* WmGlobalsAura::NewContainerWindow() {
+  aura::Window* aura_window = new aura::Window(nullptr);
+  aura_window->Init(ui::LAYER_NOT_DRAWN);
+  return WmWindowAura::Get(aura_window);
+}
+
 WmWindow* WmGlobalsAura::GetFocusedWindow() {
   return WmWindowAura::Get(
       aura::client::GetFocusClient(Shell::GetPrimaryRootWindow())
           ->GetFocusedWindow());
 }
 
 WmWindow* WmGlobalsAura::GetActiveWindow() {
   return WmWindowAura::Get(wm::GetActiveWindow());
 }
 
@@ skipping 135 matching lines @@
                     OnDisplayConfigurationChanged());
 }
 
 void WmGlobalsAura::OnOverviewModeEnded() {
   FOR_EACH_OBSERVER(WmOverviewModeObserver, overview_mode_observers_,
                     OnOverviewModeEnded());
 }
 
 }  // namespace wm
 }  // namespace ash