Add GetWebContents to ShellDelegate.

ash/mus/shell_delegate_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_SHELL_DELEGATE_MUS_H_
 #define ASH_MUS_SHELL_DELEGATE_MUS_H_
 
 #include <memory>
 
 #include "ash/common/shell_delegate.h"
@@ skipping 30 matching lines @@
   std::unique_ptr<PaletteDelegate> CreatePaletteDelegate() override;
   ui::MenuModel* CreateContextMenu(WmShelf* wm_shelf,
                                    const ShelfItem* item) override;
   GPUSupport* CreateGPUSupport() override;
   base::string16 GetProductName() const override;
   gfx::Image GetDeprecatedAcceleratorImage() const override;
   bool IsTouchscreenEnabledInPrefs(bool use_local_state) const override;
   void SetTouchscreenEnabledInPrefs(bool enabled,
                                     bool use_local_state) override;
   void UpdateTouchscreenStatusFromPrefs() override;
+  content::WebContents* GetWebContents() override;
 
  private:
   // |connector_| may be null in tests.
   service_manager::Connector* connector_;
 
   DISALLOW_COPY_AND_ASSIGN(ShellDelegateMus);
 };
 
 }  // namespace ash
 
 #endif  // ASH_MUS_SHELL_DELEGATE_MUS_H_