[js-perf-test] Add flags for async benchmark

Skip unhandled promises for AsyncAwait performance test.

Bug: v8:1099632
Change-Id: I21d69d5700860f0b05fb8c6c90ea85dc28cb3890
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2274606
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68631}

test/js-perf-test/AsyncAwait/baseline-naive-promises.js

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --ignore-unhandled-promises
-
 new BenchmarkSuite('BaselineNaivePromises', [1000], [
   new Benchmark('Basic', false, false, 0, Basic, Setup),
 ]);

test/js-perf-test/JSTests5.json

@@ -19,7 +19,7 @@
         "baseline-babel-es2017.js",
         "baseline-naive-promises.js"
       ],
-      "flags": ["--allow-natives-syntax"],
+      "flags": ["--allow-natives-syntax", "--ignore-unhandled-promises"],
       "results_regexp": "^%s\\-AsyncAwait\\(Score\\): (.+)$",
       "tests": [
         {"name": "BaselineES2017"},