message: Add profiling scoped for frontend and backend
  Summary: As title.
diff: @@ -1208,8 +1208,12 @@ int main(int argc, char* argv[]) {
  args.redex_options.min_sdk = *maybe_sdk;
  }
  + {
  + auto profile_frontend =
  + ScopedCommandProfiling::maybe_from_env("FRONTEND_", "frontend");
  redex_frontend(conf, args, *pg_config, stores, stats);
  conf.parse_global_config();
  + }
  // Initialize purity defaults, if set.
  purity::CacheConfig::parse_default(conf);
  @@ -1232,6 +1236,8 @@ int main(int argc, char* argv[]) {
  if (args.stop_pass_idx == boost::none) {
  // Call redex_backend by default
  + auto profile_backend =
  + ScopedCommandProfiling::maybe_from_env("BACKEND_", "backend");
  redex_backend(conf, manager, stores, stats);
  if (args.config.get("emit_class_method_info_map", false).asBool()) {
  dump_class_method_info_map(conf.metafile(CLASS_METHOD_INFO_MAP),
  