sync: Improve handling of bad UniquePos (retry)

sync/syncable/directory.cc

Index: sync/syncable/directory.cc
diff --git a/sync/syncable/directory.cc b/sync/syncable/directory.cc
index cebb2d4fd8401cf0410de0bf543e9c89dc55f148..e523bcdf290cec0d608792bb761b257e632d2a9e 100644
--- a/sync/syncable/directory.cc
+++ b/sync/syncable/directory.cc
@@ -167,6 +167,11 @@ DirOpenResult Directory::OpenImpl(
   // Temporary indices before kernel_ initialized in case Load fails. We 0(1)
   // swap these later.
   Directory::MetahandlesMap tmp_handles_map;
+
+  // Avoids mem leaks on failure.  Harmlessly deletes the empty hash map after
+  // the swap in the success case.
+  STLValueDeleter<Directory::MetahandlesMap> deleter(&tmp_handles_map);
+
   JournalIndex delete_journals;
 
   DirOpenResult result =