[es6] implement spread calls

src/harmony-spread.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.
+
+'use strict';
+
+function SpreadArguments() {
+  var count = %_ArgumentsLength();
+  var args = new InternalArray();
+
+  for (var i = 0; i < count; ++i) {
+    var array = %_Arguments(i);
+    var length = array.length;
+    for (var j = 0; j < length; ++j) {
+      args.push(array[j]);
+    }
+  }
+
+  return args;
+}
+
+
+function SpreadIterable(collection) {
+  if (IS_NULL_OR_UNDEFINED(collection)) {
+    throw MakeTypeError("not_iterable", [collection]);
+  }
+
+  var args = new InternalArray();
+  for (var value of collection) {
+    args.push(value);
+  }
+  return args;
+}