[Oilpan] Change pointer type to RefPtrWillBePersistent

Source/web/WebEmbeddedWorkerImpl.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 97 matching lines @@
     RefPtr<WorkerThread> m_workerThread;
     RefPtr<WorkerLoaderProxy> m_loaderProxy;
     OwnPtr<ServiceWorkerGlobalScopeProxy> m_workerGlobalScopeProxy;
     OwnPtr<WorkerInspectorProxy> m_workerInspectorProxy;
 
     // 'shadow page' - created to proxy loading requests from the worker.
     // Both WebView and WebFrame objects are close()'ed (where they're
     // deref'ed) when this EmbeddedWorkerImpl is destructed, therefore they
     // are guaranteed to exist while this object is around.
     WebView* m_webView;
-    WebLocalFrameImpl* m_mainFrame;
+    RefPtrWillBePersistent<WebLocalFrameImpl> m_mainFrame;
 
     bool m_loadingShadowPage;
     bool m_askedToTerminate;
 
     enum WaitingForDebuggerState {
         WaitingForDebuggerBeforeLoadingScript,
         WaitingForDebuggerAfterScriptLoaded,
         NotWaitingForDebugger
     };
 
     WaitingForDebuggerState m_waitingForDebuggerState;
 };
 
 } // namespace blink
 
 #endif // WebEmbeddedWorkerImpl_h