Remove DCHECK in WmWindowMus::CloseWidget()

ash/mus/bridge/wm_window_mus.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/mus/bridge/wm_window_mus.h"
 
 #include "ash/common/shelf/shelf_item_types.h"
 #include "ash/common/wm/container_finder.h"
 #include "ash/common/wm/window_positioning_utils.h"
 #include "ash/common/wm/window_state.h"
@@ skipping 57 matching lines @@
 
 WmRootWindowController* WmWindowMus::GetRootWindowController() {
   return GetRootWindowControllerMus();
 }
 
 WmShell* WmWindowMus::GetShell() const {
   return WmShellMus::Get();
 }
 
 void WmWindowMus::CloseWidget() {
-  views::Widget* widget = views::Widget::GetWidgetForNativeView(aura_window());
-  DCHECK(widget);
-  // Allow the client to service the close request for remote widgets.
+  // NOTE: in the FOR_CLIENT case there is not necessarily a widget associated
+  // with the window. Mash only creates widgets for top level windows if mash
+  // renders the non-client frame.
   if (aura_window()->GetProperty(kWidgetCreationTypeKey) ==
       WidgetCreationType::FOR_CLIENT) {
     WmShellMus::Get()->window_manager()->window_manager_client()->RequestClose(
         aura_window());
   } else {
-    widget->Close();
+    WmWindowAura::CloseWidget();
   }
 }
 
 void WmWindowMus::AddLimitedPreTargetHandler(ui::EventHandler* handler) {
   DCHECK(WmShellMus::Get()->window_tree_client()->WasCreatedByThisClient(
       aura::WindowMus::Get(aura_window())));
   WmWindowAura::AddLimitedPreTargetHandler(handler);
 }
 
 }  // namespace mus
 }  // namespace ash