Discard unused AppListPrefs code.

chrome/browser/ui/app_list/model_pref_updater.h

-// Copyright 2014 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 CHROME_BROWSER_UI_APP_LIST_MODEL_PREF_UPDATER_H_
-#define CHROME_BROWSER_UI_APP_LIST_MODEL_PREF_UPDATER_H_
-
-#include "base/macros.h"
-#include "ui/app_list/app_list_model_observer.h"
-
-namespace app_list {
-
-class AppListModel;
-class AppListPrefs;
-
-// A class which listens to an AppListModel and updates the local pref model of
-// the app list accordingly.
-class ModelPrefUpdater : public AppListModelObserver {
- public:
-  ModelPrefUpdater(AppListPrefs* app_list_prefs, AppListModel* model);
-  ~ModelPrefUpdater() override;
-
-  // Overridden from AppListModelObserver:
-  void OnAppListItemAdded(AppListItem* item) override;
-  void OnAppListItemWillBeDeleted(AppListItem* item) override;
-  void OnAppListItemUpdated(AppListItem* item) override;
-
- private:
-  void UpdatePrefsFromAppListItem(AppListItem* item);
-
-  AppListPrefs* app_list_prefs_;
-  AppListModel* model_;
-
-  DISALLOW_COPY_AND_ASSIGN(ModelPrefUpdater);
-};
-
-}  // namespace app_list
-
-#endif  // CHROME_BROWSER_UI_APP_LIST_MODEL_PREF_UPDATER_H_