message: [XLA] In the HLO parser, give the module a non-empty default name.
  Otherwise, when parsing a single instruction, the parsed module doesn't have a name, which won't pass the hlo verifier check.
diff: @@ -391,7 +391,7 @@ Status HloParser::Run(HloModule* module) {
  // This means that the text is a single HLO instruction.
  if (!ParseSingleInstruction(module)) {
  return InvalidArgument(
  - "Syntax error when trying to parse the text as single "
  + "Syntax error when trying to parse the text as a single "
  "HloInstruction:\n%s",
  GetError());
  }
  @@ -3348,14 +3348,14 @@ bool HloParser::ParseSingleInstruction(HloModule* module) {
  StatusOr<std::unique_ptr<HloModule>> ParseHloString(
  absl::string_view str, const HloModuleConfig& config) {
  - auto module = absl::make_unique<HloModule>(/*name=*/"", config);
  + auto module = absl::make_unique<HloModule>(/*name=*/"_", config);
  HloParser parser(str);
  TF_RETURN_IF_ERROR(parser.Run(module.get()));
  return std::move(module);
  }
  StatusOr<std::unique_ptr<HloModule>> ParseHloString(absl::string_view str) {
  - auto module = absl::make_unique<HloModule>(/*name=*/"", HloModuleConfig());
  + auto module = absl::make_unique<HloModule>(/*name=*/"_", HloModuleConfig());
  HloParser parser(str);
  TF_RETURN_IF_ERROR(parser.Run(module.get()));
  return std::move(module);
  