[js-perf-test] Add RegExp microbenchmarks

test/js-perf-test/RegExp/base.js

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+function benchName(bench, setup) {
+  var name = bench.name;
+  if (setup) name += "/" + setup.name;
+}
+
+function slowBenchName(bench, setup) {
+  return benchName(bench, setup) + " (Slow)";
+}
+
+function slow(setupFunction) {
+  return () => {
+    setupFunction();
+    // Trigger RegExp slow paths.
+    const regExpExec = re.exec;
+    re.exec = (str) => regExpExec.call(re, str);
+  };
+}
+
+function createHaystack() {
+  let s = "abCdefgz";
+  for (let i = 0; i < 3; i++) s += s;
+  return s;
+}
+
+function createBenchmarkSuite(name) {
+  return new BenchmarkSuite(
+    name, [1000],
+    benchmarks.map(([bench, setup]) =>
+        new Benchmark(benchName(bench, setup), false, false, 0, bench,
+                      setup)));
+}
+
+function createSlowBenchmarkSuite(name) {
+  return new BenchmarkSuite(
+    "Slow" + name, [1000],
+    benchmarks.map(([bench, setup]) =>
+        new Benchmark(slowBenchName(bench, setup), false, false, 0, bench,
+                      slow(setup))));
+}