Oilpan: fix build after r177520.

Source/modules/serviceworkers/NavigatorServiceWorker.cpp

Index: Source/modules/serviceworkers/NavigatorServiceWorker.cpp
diff --git a/Source/modules/serviceworkers/NavigatorServiceWorker.cpp b/Source/modules/serviceworkers/NavigatorServiceWorker.cpp
index 3af213969a333f70e51222b53ee5cb3a4b6b27ce..be95e639c4119eb5d4982fd5a610faa95591bc7a 100644
--- a/Source/modules/serviceworkers/NavigatorServiceWorker.cpp
+++ b/Source/modules/serviceworkers/NavigatorServiceWorker.cpp
@@ -74,4 +74,10 @@ void NavigatorServiceWorker::willDetachGlobalObjectFromFrame()
     }
 }
 
+void NavigatorServiceWorker::trace(Visitor* visitor)
+{
+    visitor->trace(m_serviceWorker);
+    WillBeHeapSupplement<Navigator>::trace(visitor);
+}
+
 } // namespace WebCore