[SyncFS] Migrate ServiceMetadata from MDDB to MDDBIndex.

chrome/browser/sync_file_system/drive_backend/drive_backend_util.h

Index: chrome/browser/sync_file_system/drive_backend/drive_backend_util.h
diff --git a/chrome/browser/sync_file_system/drive_backend/drive_backend_util.h b/chrome/browser/sync_file_system/drive_backend/drive_backend_util.h
index d5e662576b61c7ded09e8aca8b79d6fa26e89116..139f6fdd2e43f97c4876a07c54d67224fbeb1ea9 100644
--- a/chrome/browser/sync_file_system/drive_backend/drive_backend_util.h
+++ b/chrome/browser/sync_file_system/drive_backend/drive_backend_util.h
@@ -23,6 +23,7 @@ class ResourceEntry;
 }
 
 namespace leveldb {
+class DB;
 class WriteBatch;
 }
 
@@ -55,6 +56,8 @@ SyncStatusCode GDataErrorCodeToSyncStatusCode(
 bool RemovePrefix(const std::string& str, const std::string& prefix,
                   std::string* out);
 
+scoped_ptr<ServiceMetadata> InitializeServiceMetadata(leveldb::DB* db);
+
 template <typename Src, typename Dest>
 void AppendContents(const Src& src, Dest* dest) {
   dest->insert(dest->end(), src.begin(), src.end());