Oilpan: fix build after r179903.

Source/modules/serviceworkers/ServiceWorkerRegistration.cpp

 // Copyright 2014 The Chromium 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 "config.h"
 #include "ServiceWorkerRegistration.h"
 
 #include "bindings/core/v8/CallbackPromiseAdapter.h"
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptPromiseResolver.h"
@@ skipping 127 matching lines @@
     ASSERT(m_outerRegistration);
     ScriptWrappable::init(this);
 
     if (!executionContext)
         return;
     if (ServiceWorkerContainerClient* client = ServiceWorkerContainerClient::from(executionContext))
         m_provider = client->provider();
     m_outerRegistration->setProxy(this);
 }
 
+void ServiceWorkerRegistration::trace(Visitor* visitor)
+{
+    visitor->trace(m_installing);
+    visitor->trace(m_waiting);
+    visitor->trace(m_active);
+    EventTargetWithInlineData::trace(visitor);
+}
+
 } // namespace blink