[tests] add microbenchmark for %TypedArray%.prototype.copyWithin

test/js-perf-test/TypedArrays/typedarrays.js

+// Copyright 2017 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.
+
+new BenchmarkSuite('CopyWithin', [1000], [
+  new Benchmark('CopyWithin-Large', false, false, 0,
+                CopyWithinLarge, CopyWithinLargeSetup, CopyWithinLargeTearDown),
+]);
+
+var initialLargeFloat64Array = new Array(10000);
+for (var i = 0; i < 5000; ++i) {
+  initialLargeFloat64Array[i] = i;
+}
+initialLargeFloat64Array = new Float64Array(initialLargeFloat64Array);
+var largeFloat64Array;
+
+function CopyWithinLarge() {
+  largeFloat64Array.copyWithin(5000);
+}
+
+function CopyWithinLargeSetup() {
+  largeFloat64Array = new Float64Array(initialLargeFloat64Array);
+}
+
+function CopyWithinLargeTearDown() {
+  for (var i = 0; i < 5000; ++i) {
+    if (largeFloat64Array[i + 5000] !== i) {
+      throw new TypeError("Unexpected result!\n" + largeFloat64Array);
+    }
+  }
+  largeFloat64Array = void 0;
+}