// If 'reuse_existing_functions' is set, use an existing function with the
  // same name, if any.
  // If 'rewrite_subgraph_fn' is set, it is applied to each subgraph before
  // function conversion.
  Status BuildFunctionDefs(const RewriteSubgraphFn& rewrite_subgraph_fn,
                           bool reuse_existing_functions,
                           FunctionLibraryDefinition* library);