Fix RegExp.prototype.toString for incompatible receivers.

test/mjsunit/regexp.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 687 matching lines @@
 
 // Should throw. Shouldn't hit asserts in debug mode.
 assertThrows("RegExp('(*)')");
 assertThrows("RegExp('(?:*)')");
 assertThrows("RegExp('(?=*)')");
 assertThrows("RegExp('(?!*)')");
 
 // Test trimmed regular expression for RegExp.test().
 assertTrue(/.*abc/.test("abc"));
 assertFalse(/.*\d+/.test("q"));
+
+// Test that RegExp.prototype.toString() throws TypeError for
+// incompatible receivers (ES5 section 15.10.6 and 15.10.6.4).
+assertThrows("RegExp.prototype.toString.call(null)", TypeError);
+assertThrows("RegExp.prototype.toString.call(0)", TypeError);
+assertThrows("RegExp.prototype.toString.call('')", TypeError);
+assertThrows("RegExp.prototype.toString.call(false)", TypeError);
+assertThrows("RegExp.prototype.toString.call(true)", TypeError);
+assertThrows("RegExp.prototype.toString.call([])", TypeError);
+assertThrows("RegExp.prototype.toString.call({})", TypeError);
+assertThrows("RegExp.prototype.toString.call(function(){})", TypeError);