Throw if setting length of a string in strict mode.

test/mjsunit/strict-mode.js

 // Copyright 2011 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 926 matching lines @@
 
   for (var i = 0; i < 10; i ++) {
     assertThrows(function() { o[seven_smi] = "value" }, TypeError);
     assertThrows(function() { o[seven_number] = "value" }, TypeError);
     assertThrows(function() { o[seven_symbol] = "value" }, TypeError);
     assertThrows(function() { o[seven_string] = "value" }, TypeError);
   }
 
   assertEquals(o[7], 17);
 })();
+
+
+(function TestAssignmentToStringLength() {
+  "use strict";
+
+  var str_val = "string";
+  var str_obj = new String(str_val);
+  var str_cat = str_val + str_val + str_obj;
+
+  assertThrows(function() { str_val.length = 1; }, TypeError);
+  assertThrows(function() { str_obj.length = 1; }, TypeError);
+  assertThrows(function() { str_cat.length = 1; }, TypeError);
+})();