Rewrite std::string("") to std::string(), Linux edition.

sync/syncable/syncable_write_transaction.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sync/syncable/syncable_write_transaction.h"
 
 #include "sync/syncable/directory.h"
 #include "sync/syncable/directory_change_delegate.h"
 #include "sync/syncable/mutable_entry.h"
 #include "sync/syncable/transaction_observer.h"
@@ skipping 157 matching lines @@
     ENUM_CASE(INVALID);
     ENUM_CASE(SYNCER);
     ENUM_CASE(AUTHWATCHER);
     ENUM_CASE(UNITTEST);
     ENUM_CASE(VACUUM_AFTER_SAVE);
     ENUM_CASE(HANDLE_SAVE_FAILURE);
     ENUM_CASE(PURGE_ENTRIES);
     ENUM_CASE(SYNCAPI);
   };
   NOTREACHED();
-  return "";
+  return std::string();
 }
 
 #undef ENUM_CASE
 
 }  // namespace syncable
 }  // namespace syncer