[SyncFS] Migrate version management from MDDB to index classes

chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.h

Index: chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.h
diff --git a/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.h b/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.h
index 8d8c2293fff9e87c66bb0799d71d5c042135481c..7a9b066e87812cc71d8a04f3fae14506a2a14706 100644
--- a/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.h
+++ b/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.h
@@ -31,7 +31,9 @@ struct ParentIDAndTitle;
 // Maintains indexes of MetadataDatabase on disk.
 class MetadataDatabaseIndexOnDisk : public MetadataDatabaseIndexInterface {
  public:
-  explicit MetadataDatabaseIndexOnDisk(leveldb::DB* db);
+  static scoped_ptr<MetadataDatabaseIndexOnDisk>
+      Create(leveldb::DB* db, leveldb::WriteBatch* batch);
+
   virtual ~MetadataDatabaseIndexOnDisk();
 
   // MetadataDatabaseIndexInterface overrides.
@@ -84,6 +86,8 @@ class MetadataDatabaseIndexOnDisk : public MetadataDatabaseIndexInterface {
     MULTIPLE,  // Two or more entires are found.
   };
 
+  explicit MetadataDatabaseIndexOnDisk(leveldb::DB* db);
+
   // Maintain indexes from AppIDs to tracker IDs.
   void AddToAppIDIndex(const FileTracker& new_tracker,
                        leveldb::WriteBatch* batch);