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 800d55745e361302886beeb29b84ce2c3517a49c..50b93c9e630025fc19ec08572da0d85df5c76f27 100644
--- a/chrome/browser/ui/app_list/app_list_syncable_service.h
+++ b/chrome/browser/ui/app_list/app_list_syncable_service.h
@@ -127,6 +127,9 @@ class AppListSyncableService : public syncer::SyncableService,
 
   const SyncItemMap& sync_items() const { return sync_items_; }
 
+  // Returns true if sync is currently active.
+  bool is_active() const { return sync_processor_ != nullptr; }
+
   // syncer::SyncableService
   syncer::SyncMergeResult MergeDataAndStartSyncing(
       syncer::ModelType type,