[SyncFS] Migrate version management from MDDB to index classes

chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.cc

Index: chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.cc
diff --git a/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.cc b/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.cc
index fad58f9a6cb77e23e16983eae1de451cb335d023..b2597432ae4a1b6c6010b5e43018edfb0ff5e7c9 100644
--- a/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.cc
+++ b/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.cc
@@ -142,12 +142,17 @@ std::string GenerateDemotedDirtyIDKey(int64 tracker_id) {
 
 }  // namespace
 
-MetadataDatabaseIndexOnDisk::MetadataDatabaseIndexOnDisk(leveldb::DB* db)
-    : db_(db) {
-  // TODO(peria): Add UMA to measure the number of FileMetadata, FileTracker,
-  //    and AppRootId.
-  // TODO(peria): If the DB version is 3, build up index lists.
-  // TODO(peria): Read service metadata from DB.
+// static
+scoped_ptr<MetadataDatabaseIndexOnDisk>
+MetadataDatabaseIndexOnDisk::Create(
+    leveldb::DB* db, leveldb::WriteBatch* batch) {
+  DCHECK(db);
+
+  if (batch)
+    PutVersionInfoToBatch(kDatabaseOnDiskVersion, batch);
+  scoped_ptr<MetadataDatabaseIndexOnDisk>
+      index(new MetadataDatabaseIndexOnDisk(db));
+  return index.Pass();
 }
 
 MetadataDatabaseIndexOnDisk::~MetadataDatabaseIndexOnDisk() {}
@@ -552,6 +557,14 @@ MetadataDatabaseIndexOnDisk::GetAllMetadataIDs() const {
   return file_ids;
 }
 
+MetadataDatabaseIndexOnDisk::MetadataDatabaseIndexOnDisk(leveldb::DB* db)
+    : db_(db) {
+  // TODO(peria): Add UMA to measure the number of FileMetadata, FileTracker,
+  //    and AppRootId.
+  // TODO(peria): If the DB version is 3, build up index lists.
+  service_metadata_ = InitializeServiceMetadata(db_);
+}
+
 void MetadataDatabaseIndexOnDisk::AddToAppIDIndex(
     const FileTracker& tracker, leveldb::WriteBatch* batch) {
   if (!IsAppRoot(tracker)) {