Revert of [sql] Use memory-mapped I/O for sql::Connection.

sync/syncable/directory_backing_store.cc

Index: sync/syncable/directory_backing_store.cc
diff --git a/sync/syncable/directory_backing_store.cc b/sync/syncable/directory_backing_store.cc
index 3ba54e6db6c5c6efe1b9fc7d6746070bfccbae72..d49ede50b1197a6cf9fa9212732435cc26b81883 100644
--- a/sync/syncable/directory_backing_store.cc
+++ b/sync/syncable/directory_backing_store.cc
@@ -1690,10 +1690,6 @@
   db_->set_exclusive_locking();
   db_->set_cache_size(32);
   db_->set_page_size(database_page_size_);
-
-  // TODO(shess): Sync corruption tests interact poorly with mmap, disable for
-  // now.  http://crbug.com/533682
-  db_->set_mmap_disabled();
   if (!catastrophic_error_handler_.is_null())
     SetCatastrophicErrorHandler(catastrophic_error_handler_);
 }