Use [[DefineOwnProperty]] to put 'constructor' field on the protoype object.

test/mjsunit/mjsunit.js

 // Copyright 2008 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 86 matching lines @@
         return false;
       }
     }
     return true;
   } else {
     return deepObjectEquals(a, b);
   }
 }
 
 
+function assertSame(expected, found, name_opt) {
+  if (found !== expected) {
+    fail(expected, found, name_opt);
+  }
+}
+
+
 function assertEquals(expected, found, name_opt) {
   if (!deepEquals(found, expected)) {
     fail(expected, found, name_opt);
   }
 }
 
 
 function assertArrayEquals(expected, found, name_opt) {
   var start = "";
   if (name_opt) {
@@ skipping 80 matching lines @@
 
 
 function assertUnreachable(name_opt) {
   // Fix this when we ditch the old test runner.
   var message = "Fail" + "ure: unreachable"
   if (name_opt) {
     message += " - " + name_opt;
   }
   throw new MjsUnitAssertionError(message);
 }