[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 d49ede50b1197a6cf9fa9212732435cc26b81883..3ba54e6db6c5c6efe1b9fc7d6746070bfccbae72 100644
--- a/sync/syncable/directory_backing_store.cc
+++ b/sync/syncable/directory_backing_store.cc
@@ -1690,6 +1690,10 @@ void DirectoryBackingStore::ResetAndCreateConnection() {
   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_);
 }