message: Avoid copying a FunctionDef in CapturedFunction.
  The recently added `FunctionLibraryDefinition::CopyFunctionDefFrom()` method performs a more efficient shallow copy.
diff: @@ -207,8 +207,7 @@ Status CreateFunctionLibraryDefinition(
  }
  *result = absl::make_unique<FunctionLibraryDefinition>(
  lib_def->ReachableDefinitions(*fdef));
  - TF_RETURN_IF_ERROR((*result)->AddFunctionDef(*fdef));
  - return Status::OK();
  + return (*result)->CopyFunctionDefFrom(func_name, *lib_def);
  }
  } // namespace
  