[SyncFS] Make on-disk version default for metadata database index

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 99e967b00e82e5d17cf528e31dd85f74af3bfede..aec156fae1ffde76b8c1fdca3cc850f5760ea68b 100644
--- a/chrome/browser/sync_file_system/drive_backend/metadata_database.h
+++ b/chrome/browser/sync_file_system/drive_backend/metadata_database.h
@@ -139,6 +139,7 @@ class MetadataDatabase {
       const CreateCallback& callback);
   static SyncStatusCode CreateForTesting(
       scoped_ptr<LevelDBWrapper> db,
+      bool enable_on_disk_index,
       scoped_ptr<MetadataDatabase>* metadata_database_out);
 
   ~MetadataDatabase();
@@ -358,6 +359,7 @@ class MetadataDatabase {
   MetadataDatabase(
       const scoped_refptr<base::SequencedTaskRunner>& worker_task_runner,
       const base::FilePath& database_path,
+      bool enable_on_disk_index,
       leveldb::Env* env_override);
   static void CreateOnWorkerTaskRunner(
       scoped_ptr<CreateParam> create_param,
@@ -418,6 +420,8 @@ class MetadataDatabase {
   leveldb::Env* env_override_;
   scoped_ptr<LevelDBWrapper> db_;
 
+  bool enable_on_disk_index_;
+
   int64 largest_known_change_id_;
 
   scoped_ptr<MetadataDatabaseIndexInterface> index_;