Oilpan: address ScrollableArea-induced build breakage from r194957.

Source/core/frame/FrameHost.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 84 matching lines @@
     static const int maxNumberOfFrames = 1000;
     void incrementSubframeCount() { ++m_subframeCount; }
     void decrementSubframeCount() { ASSERT(m_subframeCount); --m_subframeCount; }
     int subframeCount() const;
 
 private:
     explicit FrameHost(Page&);
 
     RawPtrWillBeMember<Page> m_page;
     const OwnPtrWillBeMember<TopControls> m_topControls;
-    const OwnPtrWillBeMember<PinchViewport> m_pinchViewport;
+    const OwnPtr<PinchViewport> m_pinchViewport;
     const OwnPtrWillBeMember<EventHandlerRegistry> m_eventHandlerRegistry;
     const OwnPtrWillBeMember<ConsoleMessageStorage> m_consoleMessageStorage;
 
     AtomicString m_overrideEncoding;
     int m_subframeCount;
 };
 
 }
 
 #endif // FrameHost_h