[es6] Perform the IsConstructor test in GetSuperConstructor.

test/webkit/class-syntax-super.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 60 matching lines @@
 shouldThrow('(new x).method2()', '"ReferenceError: Unsupported reference to \'super\'"');
 shouldBeTrue('new (class { constructor() { return undefined; } }) instanceof Object');
 shouldBeTrue('new (class { constructor() { return 1; } }) instanceof Object');
 shouldThrow('new (class extends Base { constructor() { return undefined } })');
 shouldBeTrue('new (class extends Base { constructor() { super(); return undefined } }) instanceof Object');
 shouldBe('x = { }; new (class extends Base { constructor() { return x } });', 'x');
 shouldBeFalse('x instanceof Base');
 shouldThrow('new (class extends Base { constructor() { } })', '"ReferenceError: this is not defined"');
 shouldThrow('new (class extends Base { constructor() { return 1; } })', '"TypeError: Derived constructors may only return object or undefined"');
 shouldThrow('new (class extends null { constructor() { return undefined } })');
-shouldThrow('new (class extends null { constructor() { super(); return undefined } })', '"TypeError: super is not a constructor"');
+shouldThrow('new (class extends null { constructor() { super(); return undefined } })', '"TypeError: Super constructor null of anonymous class is not a constructor"');
 shouldBe('x = { }; new (class extends null { constructor() { return x } });', 'x');
 shouldBeTrue('x instanceof Object');
 shouldThrow('new (class extends null { constructor() { } })', '"ReferenceError: this is not defined"');
 shouldThrow('new (class extends null { constructor() { return 1; } })', '"TypeError: Derived constructors may only return object or undefined"');
-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('new (class { constructor() { super() } })', '"SyntaxError: \'super\' keyword unexpected here"');
 shouldThrow('function x() { super(); }', '"SyntaxError: \'super\' keyword unexpected here"');
 shouldThrow('new (class extends Object { constructor() { function x() { super() } } })', '"SyntaxError: \'super\' keyword unexpected here"');
 shouldThrow('new (class extends Object { constructor() { function x() { super.method } } })', '"SyntaxError: \'super\' keyword unexpected here"');
 shouldThrow('function x() { super.method(); }', '"SyntaxError: \'super\' keyword unexpected here"');
 shouldThrow('function x() { super(); }', '"SyntaxError: \'super\' keyword unexpected here"');
 
 var successfullyParsed = true;