ArrayUnshift() should not modify length of a frozen object.

src/array.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 645 matching lines @@
   } else {
     if (num_arguments == 0 && $Object.isFrozen(this)) {
       // In the zero argument case, values from the prototype come into the
       // object. This can't be allowed on frozen arrays.
       for (var i = 0; i < len; i++) {
         if (!this.hasOwnProperty(i) && !IS_UNDEFINED(this[i])) {
           throw MakeTypeError("array_functions_on_frozen",
                               ["Array.prototype.shift"]);
         }
       }
+      return this.length;
     }
 
     SimpleMove(this, 0, 0, len, num_arguments);
   }
 
   for (var i = 0; i < num_arguments; i++) {
     this[i] = %_Arguments(i);
   }
 
   this.length = len + num_arguments;
@@ skipping 959 matching lines @@
   ));
 
   SetUpLockedPrototype(InternalPackedArray, $Array(), $Array(
     "join", getFunction("join", ArrayJoin),
     "pop", getFunction("pop", ArrayPop),
     "push", getFunction("push", ArrayPush)
   ));
 }
 
 SetUpArray();