Implement SyncEngine::UpdateRegisteredApps()

chrome/browser/sync_file_system/drive_backend/metadata_database.h

Index: chrome/browser/sync_file_system/drive_backend/metadata_database.h
diff --git a/chrome/browser/sync_file_system/drive_backend/metadata_database.h b/chrome/browser/sync_file_system/drive_backend/metadata_database.h
index b92dd09912d1d442bb4f30b6d447bdfc504407a8..da2049aa11c022e4229d33b0f449de86772d4cd4 100644
--- a/chrome/browser/sync_file_system/drive_backend/metadata_database.h
+++ b/chrome/browser/sync_file_system/drive_backend/metadata_database.h
@@ -253,6 +253,9 @@ class MetadataDatabase {
   // Assigns the dirty tracker if exists and |tracker| is non-NULL.
   bool GetLowPriorityDirtyTracker(FileTracker* tracker);
 
+  // Sets |app_ids| to a list of all registered app ids.
+  void GetRegisteredAppIDs(std::vector<std::string>* app_ids);
+
  private:
   friend class ListChangesTaskTest;
   friend class MetadataDatabaseTest;