Implement local storage for App List in case app sync is off.

chrome/browser/ui/app_list/app_list_syncable_service.h

Index: chrome/browser/ui/app_list/app_list_syncable_service.h
diff --git a/chrome/browser/ui/app_list/app_list_syncable_service.h b/chrome/browser/ui/app_list/app_list_syncable_service.h
index 7900f3f664833b85aa6288a0a3d50d218c706599..32649f3ecbbbea6035af63cb71e4718b8d261adf 100644
--- a/chrome/browser/ui/app_list/app_list_syncable_service.h
+++ b/chrome/browser/ui/app_list/app_list_syncable_service.h
@@ -39,6 +39,10 @@ namespace sync_pb {
 class AppListSpecifics;
 }
 
+namespace user_prefs {
+class PrefRegistrySyncable;
+}
+
 namespace app_list {
 
 class AppListFolderItem;
@@ -81,6 +85,9 @@ class AppListSyncableService : public syncer::SyncableService,
 
   ~AppListSyncableService() override;
 
+  // Registers prefs to support local storage.
+  static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
+
   // Adds |item| to |sync_items_| and |model_|. If a sync item already exists,
   // updates the existing sync item instead.
   void AddItem(std::unique_ptr<AppListItem> app_item);
@@ -229,6 +236,10 @@ class AppListSyncableService : public syncer::SyncableService,
   // an OEM (extension->was_installed_by_oem() is true).
   bool AppIsOem(const std::string& id);
 
+  // Initializes sync items from the local storage while sync service is not
+  // enabled.
+  void InitFromLocalStorage();
+
   // Helper that notifies observers that sync model has been updated.
   void NotifyObserversSyncUpdated();