[es6] Introduce spec compliant IsConstructor.

src/runtime/runtime-object.cc

Index: src/runtime/runtime-object.cc
diff --git a/src/runtime/runtime-object.cc b/src/runtime/runtime-object.cc
index d00ce5276d6ae9fcce0524c278ad8a4652499c3a..b128190fb546a1c1b1a03d4ed9e6167c691ad11d 100644
--- a/src/runtime/runtime-object.cc
+++ b/src/runtime/runtime-object.cc
@@ -1056,9 +1056,8 @@ static Object* Runtime_NewObjectHelper(Isolate* isolate,
       Handle<JSFunction>::cast(original_constructor);
 
 
-  // If function should not have prototype, construction is not allowed. In this
-  // case generated code bailouts here, since function has no initial_map.
-  if (!function->should_have_prototype() && !function->shared()->bound()) {
+  // Check that function is a constructor.
+  if (!function->IsConstructor()) {
     THROW_NEW_ERROR_RETURN_FAILURE(
         isolate, NewTypeError(MessageTemplate::kNotConstructor, constructor));
   }