Fixed RegExp.prototype.toString.call bug not throwing TypeError when non RegExp object was passed.

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
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@@ 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"));
+
+// ES5.1, 15.10.6 conformance tests
+assertThrows("RegExp.prototype.toString.call(null)");
+assertThrows("RegExp.prototype.toString.call(0)");
+assertThrows("RegExp.prototype.toString.call('')");
+assertThrows("RegExp.prototype.toString.call(false)");
+assertThrows("RegExp.prototype.toString.call(true)");
+assertThrows("RegExp.prototype.toString.call([])");
+assertThrows("RegExp.prototype.toString.call({})");
+assertThrows("RegExp.prototype.toString.call(function(){})");