mash: Refactor ChromeLauncherController's ShelfDelegate code.

ash/mus/shelf_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_SHELF_DELEGATE_MUS_H_
 #define ASH_MUS_SHELF_DELEGATE_MUS_H_
 
 #include <string>
 
 #include "ash/common/shelf/shelf_delegate.h"
 #include "ash/public/cpp/shelf_types.h"
 #include "base/macros.h"
 
 namespace ash {
 
 // Manages communication between the mash shelf and the browser.
 class ShelfDelegateMus : public ShelfDelegate {
  public:
   ShelfDelegateMus();
   ~ShelfDelegateMus() override;
 
  private:
   // ShelfDelegate:
   ShelfID GetShelfIDForAppID(const std::string& app_id) override;
   ShelfID GetShelfIDForAppIDAndLaunchID(const std::string& app_id,
                                         const std::string& launch_id) override;
-  bool HasShelfIDToAppIDMapping(ShelfID id) const override;
   const std::string& GetAppIDForShelfID(ShelfID id) override;
   void PinAppWithID(const std::string& app_id) override;
   bool IsAppPinned(const std::string& app_id) override;
   void UnpinAppWithID(const std::string& app_id) override;
 
   DISALLOW_COPY_AND_ASSIGN(ShelfDelegateMus);
 };
 
 }  // namespace ash
 
 #endif  // ASH_MUS_SHELF_DELEGATE_MUS_H_