Oilpan: extend tracing over WebFrame trees.

Source/web/OpenedFrameTracker.h

 // 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.
 
 #ifndef OpenedFrameTracker_h
 #define OpenedFrameTracker_h
 
 #include "wtf/HashSet.h"
 #include "wtf/Noncopyable.h"
 
 namespace blink {
 
+class Visitor;
 class WebFrame;
 
 // Small helper class to track the set of frames that a WebFrame has opened.
 // Due to layering restrictions, we need to hide the implementation, since
 // public/web/ cannot depend on wtf/.
 class OpenedFrameTracker {
     WTF_MAKE_NONCOPYABLE(OpenedFrameTracker);
 public:
     OpenedFrameTracker();
     ~OpenedFrameTracker();
 
     bool isEmpty() const;
     void add(WebFrame*);
     void remove(WebFrame*);
 
     // Updates the opener for all tracked frames.
     void updateOpener(WebFrame*);
 
+    void traceFrames(Visitor*);
+
 private:
     WTF::HashSet<WebFrame*> m_openedFrames;
 };
 
 } // namespace blink
 
 #endif // WebFramePrivate_h