[es6] Re-implement rest parameters via desugaring.

test/mjsunit/harmony/regress/regress-508074.js

+// Copyright 2015 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.
+
+// Flags: --harmony-rest-parameters --harmony-arrow-functions
+// Flags: --allow-natives-syntax
+
+var f = (a, b, ...c) => {
+  print(a);
+  print(b);
+  print(c);
+  assertEquals(6, a);
+  assertEquals(5, b);
+  assertEquals([4, 3, 2, 1], c);
+};
+
+function g() {
+  f(6, 5, 4, 3, 2, 1);
+};
+
+g();
+g();
+g();
+
+%OptimizeFunctionOnNextCall(g);
+g();