[Turbofan] Add benchmark for String.prototype.charCodeAt

This also fixes benchmark scores for String.prototype.indexOf

Bug: v8:7127, v8:7092
Change-Id: Iee0f9689feb5923b300e253c267a6f32ffd4da20
Reviewed-on: https://chromium-review.googlesource.com/846739Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50316}

test/js-perf-test/Strings/string-indexof.js

@@ -2,17 +2,16 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-new BenchmarkSuite('StringIndexOfConstant', [1000], [
+new BenchmarkSuite('StringIndexOfConstant', [5], [
   new Benchmark('StringIndexOfConstant', true, false, 0,
   StringIndexOfConstant),
 ]);
 
-new BenchmarkSuite('StringIndexOfNonConstant', [1000], [
+new BenchmarkSuite('StringIndexOfNonConstant', [5], [
   new Benchmark('StringIndexOfNonConstant', true, false, 0,
   StringIndexOfNonConstant),
 ]);
 
-const N = 10 ** 6;
 const subject = "aaaaaaaaaaaaaaaab";
 const searches = ['a', 'b', 'c'];
 
@@ -35,3 +34,36 @@ function StringIndexOfNonConstant() {
 
   return sum;
 }
+
+new BenchmarkSuite('StringCharCodeAtConstant', [3], [
+  new Benchmark('StringIndexOfConstant', true, false, 0,
+  StringCharCodeAtConstant),
+]);
+
+new BenchmarkSuite('StringCharCodeAtNonConstant', [3], [
+  new Benchmark('StringIndexOfNonConstant', true, false, 0,
+  StringCharCodeAtNonConstant),
+]);
+
+const string = "qweruiplkjhgfdsazxccvbnm";
+const indices = [1, 13, 32, 100, "xx"];
+
+function StringCharCodeAtConstant() {
+  var sum = 0;
+
+  for (var j = 0; j < indices.length - 1; ++j) {
+    sum += string.charCodeAt(indices[j] | 0);
+  }
+
+  return sum;
+}
+
+function StringCharCodeAtNonConstant() {
+  var sum = 0;
+
+  for (var j = 0; j < indices.length - 1; ++j) {
+    sum += string.charCodeAt(indices[j]);
+  }
+
+  return sum;
+}