Eliminate ash::Shell access in ShelfView

ash/mus/bridge/wm_shell_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_SHELL_MUS_H_
 #define ASH_MUS_BRIDGE_WM_SHELL_MUS_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 54 matching lines @@
   bool IsActiveDisplayId(int64_t display_id) const override;
   bool IsForceMaximizeOnFirstRun() override;
   bool IsPinned() override;
   void SetPinnedWindow(WmWindow* window) override;
   bool CanShowWindowForUser(WmWindow* window) override;
   void LockCursor() override;
   void UnlockCursor() override;
   std::vector<WmWindow*> GetAllRootWindows() override;
   void RecordUserMetricsAction(UserMetricsAction action) override;
   void RecordTaskSwitchMetric(TaskSwitchSource source) override;
+  void ShowContextMenu(const gfx::Point& location_in_screen,
+                       ui::MenuSourceType source_type) override;
   std::unique_ptr<WindowResizer> CreateDragWindowResizer(
       std::unique_ptr<WindowResizer> next_window_resizer,
       wm::WindowState* window_state) override;
   std::unique_ptr<WindowCycleEventFilter> CreateWindowCycleEventFilter()
       override;
   std::unique_ptr<wm::MaximizeModeEventHandler> CreateMaximizeModeEventHandler()
       override;
   std::unique_ptr<ScopedDisableInternalMouseAndKeyboard>
   CreateScopedDisableInternalMouseAndKeyboard() override;
   void OnOverviewModeStarting() override;
@@ skipping 32 matching lines @@
 
   base::ObserverList<WmActivationObserver> activation_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(WmShellMus);
 };
 
 }  // namespace mus
 }  // namespace ash
 
 #endif  // ASH_MUS_BRIDGE_WM_SHELL_MUS_H_