mash shelf: Don't create shelf DimmerView in ShelfWidget on mus

ash/mus/bridge/wm_shelf_mus.h

 // 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.
 
 #ifndef ASH_MUS_BRIDGE_WM_SHELF_MUS_H_
 #define ASH_MUS_BRIDGE_WM_SHELF_MUS_H_
 
 #include <stdint.h>
 
 #include <vector>
@@ skipping 15 matching lines @@
 
   // WmShelf:
   WmWindow* GetWindow() override;
   ShelfAlignment GetAlignment() const override;
   void SetAlignment(ShelfAlignment alignment) override;
   ShelfAutoHideBehavior GetAutoHideBehavior() const override;
   void SetAutoHideBehavior(ShelfAutoHideBehavior behavior) override;
   ShelfAutoHideState GetAutoHideState() const override;
   void UpdateAutoHideState() override;
   ShelfBackgroundType GetBackgroundType() const override;
+  WmDimmerView* CreateDimmerView(bool disable_animations_for_test) override;
   bool IsDimmed() const override;
   bool IsShowingOverflowBubble() const override;
   void SchedulePaint() override;
   bool IsVisible() const override;
   void UpdateVisibilityState() override;
   ShelfVisibilityState GetVisibilityState() const override;
   gfx::Rect GetIdealBounds() override;
   gfx::Rect GetUserWorkAreaBounds() const override;
   void UpdateIconPositionForWindow(WmWindow* window) override;
   gfx::Rect GetScreenBoundsOfItemIconForWindow(WmWindow* window) override;
   bool ProcessGestureEvent(const ui::GestureEvent& event) override;
   void AddObserver(WmShelfObserver* observer) override;
   void RemoveObserver(WmShelfObserver* observer) override;
   void SetKeyboardBoundsForTesting(const gfx::Rect& bounds) override;
   ShelfLockingManager* GetShelfLockingManagerForTesting() override;
   ShelfView* GetShelfViewForTesting() override;
 
  private:
   base::ObserverList<WmShelfObserver> observers_;
 
   ShelfLayoutManager* shelf_layout_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(WmShelfMus);
 };
 
 }  // namespace mus
 }  // namespace ash
 
 #endif  // ASH_MUS_BRIDGE_WM_SHELF_MUS_H_