[es6] Introduce spec compliant IsConstructor.

src/runtime/runtime-classes.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/runtime/runtime-utils.h"
 
 #include <stdlib.h>
 #include <limits>
 
 #include "src/arguments.h"
@@ skipping 87 matching lines @@
                                        Handle<JSFunction> constructor,
                                        int start_position, int end_position) {
   Handle<Object> prototype_parent;
   Handle<Object> constructor_parent;
 
   if (super_class->IsTheHole()) {
     prototype_parent = isolate->initial_object_prototype();
   } else {
     if (super_class->IsNull()) {
       prototype_parent = isolate->factory()->null_value();
-    } else if (super_class->IsJSFunction()) {  // TODO(bmeurer): IsConstructor.
-      if (Handle<JSFunction>::cast(super_class)->shared()->is_generator()) {
+    } else if (super_class->IsConstructor()) {
+      if (super_class->IsJSFunction() &&
+          Handle<JSFunction>::cast(super_class)->shared()->is_generator()) {
         THROW_NEW_ERROR(
             isolate,
             NewTypeError(MessageTemplate::kExtendsValueGenerator, super_class),
             Object);
       }
       ASSIGN_RETURN_ON_EXCEPTION(
           isolate, prototype_parent,
           Runtime::GetObjectProperty(isolate, super_class,
                                      isolate->factory()->prototype_string(),
                                      SLOPPY),
@@ skipping 402 matching lines @@
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
       isolate, result,
       Execution::New(isolate, super_constructor, original_constructor,
                      argument_count, arguments.get()));
 
   return *result;
 }
 
 }  // namespace internal
 }  // namespace v8