mash: Refactor ChromeLauncherController's ShelfDelegate code.

ash/mus/shelf_delegate_mus.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/mus/shelf_delegate_mus.h"
 
 #include "ash/common/shelf/shelf_controller.h"
 #include "ash/shell.h"
 #include "base/strings/string_util.h"
 
@@ skipping 11 matching lines @@
     return Shell::Get()->shelf_controller()->app_id_to_shelf_id().at(app_id);
   return 0;
 }
 
 ShelfID ShelfDelegateMus::GetShelfIDForAppIDAndLaunchID(
     const std::string& app_id,
     const std::string& launch_id) {
   return ShelfDelegateMus::GetShelfIDForAppID(app_id);
 }
 
-bool ShelfDelegateMus::HasShelfIDToAppIDMapping(ShelfID id) const {
-  return Shell::Get()->shelf_controller()->shelf_id_to_app_id().count(id) > 0;
-}
-
 const std::string& ShelfDelegateMus::GetAppIDForShelfID(ShelfID id) {
   if (Shell::Get()->shelf_controller()->shelf_id_to_app_id().count(id))
     return Shell::Get()->shelf_controller()->shelf_id_to_app_id().at(id);
   return base::EmptyString();
 }
 
 void ShelfDelegateMus::PinAppWithID(const std::string& app_id) {
   NOTIMPLEMENTED();
 }
 
 bool ShelfDelegateMus::IsAppPinned(const std::string& app_id) {
   NOTIMPLEMENTED();
   return false;
 }
 
 void ShelfDelegateMus::UnpinAppWithID(const std::string& app_id) {
   NOTIMPLEMENTED();
 }
 
 }  // namespace ash