[strong] dot prototypes of strong class literals should be strong objects

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 <stdlib.h>
 #include <limits>
 
 #include "src/v8.h"
 
 #include "src/arguments.h"
@@ skipping 119 matching lines @@
       // TODO(arv): Should be IsConstructor.
       THROW_NEW_ERROR(
           isolate,
           NewTypeError(MessageTemplate::kExtendsValueNotFunction, super_class),
           Object);
     }
   }
 
   Handle<Map> map =
       isolate->factory()->NewMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
+  if (constructor->map()->is_strong()) {
+    map->set_is_strong();
+  }
   Map::SetPrototype(map, prototype_parent);
   map->SetConstructor(*constructor);
   Handle<JSObject> prototype = isolate->factory()->NewJSObjectFromMap(map);
 
   Handle<String> name_string = name->IsString()
                                    ? Handle<String>::cast(name)
                                    : isolate->factory()->empty_string();
   constructor->shared()->set_name(*name_string);
 
   if (!super_class->IsTheHole()) {
@@ skipping 440 matching lines @@
   Handle<Object> result;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
       isolate, result,
       Execution::Call(isolate, reflect, isolate->factory()->undefined_value(),
                       arraysize(argv), argv));
 
   return *result;
 }
 }  // namespace internal
 }  // namespace v8