[es6] Introduce spec compliant IsConstructor.

src/api-natives.cc

 // Copyright 2015 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/api-natives.h"
 
 #include "src/api.h"
 #include "src/isolate-inl.h"
 #include "src/lookup.h"
 #include "src/messages.h"
@@ skipping 476 matching lines @@
   if (!obj->named_property_handler()->IsUndefined()) {
     map->set_has_named_interceptor();
   }
   if (!obj->indexed_property_handler()->IsUndefined()) {
     map->set_has_indexed_interceptor();
   }
 
   // Mark instance as callable in the map.
   if (!obj->instance_call_handler()->IsUndefined()) {
     map->set_is_callable();
+    map->set_is_constructor(true);
   }
 
   // Recursively copy parent instance templates' accessors,
   // 'data' may be modified.
   int max_number_of_additional_properties = 0;
   int max_number_of_static_properties = 0;
   FunctionTemplateInfo* info = *obj;
   while (true) {
     if (!info->instance_template()->IsUndefined()) {
       Object* props = ObjectTemplateInfo::cast(info->instance_template())
@@ skipping 54 matching lines @@
     Handle<AccessorInfo> accessor(AccessorInfo::cast(array->get(i)));
     JSObject::SetAccessor(result, accessor).Assert();
   }
 
   DCHECK(result->shared()->IsApiFunction());
   return result;
 }
 
 }  // namespace internal
 }  // namespace v8