Add performance tests for Map/Set with String and Object keys

test/js-perf-test/Collections/common.js

+// Copyright 2014 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.
+
+
+var N = 10;
+var keys;
+
+
+function SetupSmiKeys() {
+  keys = new Array(N * 2);
+  for (var i = 0; i < N * 2; i++) {
+    keys[i] = i;
+  }
+}
+
+
+function SetupStringKeys() {
+  keys = new Array(N * 2);
+  for (var i = 0; i < N * 2; i++) {
+    keys[i] = 's' + i;
+  }
+}
+
+
+function SetupObjectKeys() {
+  keys = new Array(N * 2);
+  for (var i = 0; i < N * 2; i++) {
+    keys[i] = {};
+  }
+}