message: Make ReachableFunctionLibraryDefinition deterministic in its output by replacing absl::flat_hash_set with std::set.
diff: @@ -1453,11 +1453,11 @@ namespace {
  constexpr char kApiImplements[] = "api_implements";
  -absl::flat_hash_set<string> ReachableFunctions(
  +std::set<string> ReachableFunctions(
  const FunctionLibraryDefinition& flib,
  const protobuf::RepeatedPtrField<NodeDef>& nodes) {
  // Functions that are reachable from the graph.
  - absl::flat_hash_set<string> reachable_funcs;
  + std::set<string> reachable_funcs;
  // For any functions, if it has attribute "api_implements" =
  // "some_interface" and it is reachable, then it means any other
  @@ -1547,7 +1547,7 @@ absl::flat_hash_set<string> ReachableFunctions(
  FunctionLibraryDefinition ReachableFunctionLibraryDefinition(
  const FunctionLibraryDefinition& flib,
  const protobuf::RepeatedPtrField<NodeDef>& nodes) {
  - absl::flat_hash_set<string> reachable_funcs = ReachableFunctions(flib, nodes);
  + std::set<string> reachable_funcs = ReachableFunctions(flib, nodes);
  FunctionLibraryDefinition reachable_flib(flib.default_registry(),
  FunctionDefLibrary());
  