Consistently use "use strict" where possible.

src/collection-iterator.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.
 
-'use strict';
+"use strict";
 
 
 // This file relies on the fact that the following declaration has been made
 // in runtime.js:
 // var $Set = global.Set;
 // var $Map = global.Map;
 
 
 function SetIteratorConstructor(set, kind) {
   %SetIteratorInitialize(this, set, kind);
@@ skipping 173 matching lines @@
   InstallFunctions($Map.prototype, DONT_ENUM, $Array(
     'entries', MapEntries,
     'keys', MapKeys,
     'values', MapValues
   ));
 
   %AddNamedProperty($Map.prototype, symbolIterator, MapEntries, DONT_ENUM);
 }
 
 ExtendMapPrototype();