[es6] Perform the IsConstructor test in GetSuperConstructor.

test/webkit/class-syntax-call.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions
 // are met:
 // 1.  Redistributions of source code must retain the above copyright
 //     notice, this list of conditions and the following disclaimer.
 // 2.  Redistributions in binary form must reproduce the above copyright
 //     notice, this list of conditions and the following disclaimer in the
@@ skipping 14 matching lines @@
 
 class A { constructor() {} };
 class B extends A { constructor() { super() } };
 
 shouldNotThrow('new A');
 shouldThrow('A()', '"TypeError: Class constructor A cannot be invoked without \'new\'"');
 shouldNotThrow('new B');
 shouldThrow('B()', '"TypeError: Class constructor B cannot be invoked without \'new\'"');
 shouldNotThrow('new (class { constructor() {} })()');
 shouldThrow('(class { constructor() {} })()', '"TypeError: Class constructor  cannot be invoked without \'new\'"');
-shouldThrow('new (class extends null { constructor() { super() } })()', '"TypeError: super is not a constructor"');
+shouldThrow('new (class extends null { constructor() { super() } })()', '"TypeError: Super constructor null of anonymous class is not a constructor"');
 shouldThrow('(class extends null { constructor() { super() } })()', '"TypeError: Class constructor  cannot be invoked without \'new\'"');
 
 var successfullyParsed = true;