message: [XLA] Refactor formatting lambda.
diff: @@ -311,11 +311,8 @@ class HloPrintOptions {
  FormatInstructionFunc format_instruction_ = [](const HloInstruction* instr,
  const string& instr_name,
  int indent, bool is_root) {
  - string tab;
  - for (int i = 0; i < indent; i++) {
  - tab += " ";
  - }
  - return tab + (is_root ? "ROOT " : "") + instr_name;
  + return absl::StrCat(string(2 * indent, ' '), is_root ? "ROOT " : "",
  + instr_name);
  };
  HloComputationPredicate print_computation_ = [](const HloComputation* comp) {
  return true;
  