Clear opener when frame is detached.

third_party/WebKit/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*);
 
   // Helper used when swapping a frame into the frame tree: this updates the
   // opener for opened frames to point to the new frame being swapped in.
   void transferTo(WebFrame*);
 
-  void traceFrames(Visitor*);
+  // Helper function to clear the openers when the frame is being detached.
+  void dispose() { transferTo(nullptr); }
 
  private:
   WTF::HashSet<WebFrame*> m_openedFrames;
 };
 
 }  // namespace blink
 
 #endif  // WebFramePrivate_h