Enable ash window cycle UI by default.

ash/wm/window_mirror_view.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/window_mirror_view.h"
 
 #include "ash/aura/wm_window_aura.h"
 #include "ash/common/wm/forwarding_layer_delegate.h"
 #include "ash/common/wm/window_state.h"
 #include "ash/wm/window_state_aura.h"
@@ skipping 86 matching lines @@
   }
 
   Layout();
 }
 
 ui::Layer* WindowMirrorView::GetMirrorLayer() {
   return layer_owner_->root();
 }
 
 gfx::Rect WindowMirrorView::GetClientAreaBounds() const {
+  // The target window may not have a widget in unit tests.
+  if (!target_->GetInternalWidget())
+    return gfx::Rect();
   views::View* client_view = target_->GetInternalWidget()->client_view();
   return client_view->ConvertRectToWidget(client_view->GetLocalBounds());
 }
 
 }  // namespace wm
 }  // namespace ash