[es6] Perform the IsConstructor test in GetSuperConstructor.

test/webkit/class-syntax-call.js

Index: test/webkit/class-syntax-call.js
diff --git a/test/webkit/class-syntax-call.js b/test/webkit/class-syntax-call.js
index 747b0ebff8c9ec760a95703996c3cc4774b3bc60..7ded66fb3fff8f953df1371887202adb01f733e7 100644
--- a/test/webkit/class-syntax-call.js
+++ b/test/webkit/class-syntax-call.js
@@ -32,7 +32,7 @@ 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;