Consistently use "use strict" where possible.

src/harmony-classes.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.
 //
 // This file relies on the fact that the following declarations have been made
 // in runtime.js:
 // var $Function = global.Function;
 // var $Array = global.Array;
 
+"use strict";
+
 
 (function() {
   function FunctionToMethod(homeObject) {
     if (!IS_SPEC_FUNCTION(this)) {
       throw MakeTypeError('toMethod_non_function',
                           [%ToString(this), typeof this]);
 
     }
 
     if (!IS_SPEC_OBJECT(homeObject)) {
       throw MakeTypeError('toMethod_non_object',
                           [%ToString(homeObject)]);
     }
 
     return %ToMethod(this, homeObject);
   }
 
   %CheckIsBootstrapping();
 
   InstallFunctions($Function.prototype, DONT_ENUM, $Array(
       "toMethod", FunctionToMethod
   ));
 }());