Wrap harmony implementations in functions.

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.
 
+var $spreadArguments;
+var $spreadIterable;
+
+(function() {
+
 '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;
 }
+
+$spreadArguments = SpreadArguments;
+$spreadIterable = SpreadIterable;
+
+})();