[es6] Perform the IsConstructor test in GetSuperConstructor.

test/webkit/class-syntax-super.js

Index: test/webkit/class-syntax-super.js
diff --git a/test/webkit/class-syntax-super.js b/test/webkit/class-syntax-super.js
index d70f2a1b2bc512f1a586096262bebbb9da81c355..5216b835364ff63bf5680a03906613676f0c5e9b 100644
--- a/test/webkit/class-syntax-super.js
+++ b/test/webkit/class-syntax-super.js
@@ -78,12 +78,12 @@ 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"');