Clear opener when frame is detached.

third_party/WebKit/Source/web/OpenedFrameTracker.cpp

 // 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.
 
 #include "web/OpenedFrameTracker.h"
 
 #include "platform/heap/Handle.h"
 #include "public/web/WebFrame.h"
 
 namespace blink {
 
 OpenedFrameTracker::OpenedFrameTracker() {}
 
-OpenedFrameTracker::~OpenedFrameTracker() {}
+OpenedFrameTracker::~OpenedFrameTracker() {
+  DCHECK(isEmpty());
+}
 
 bool OpenedFrameTracker::isEmpty() const {
   return m_openedFrames.isEmpty();
 }
 
 void OpenedFrameTracker::add(WebFrame* frame) {
   m_openedFrames.insert(frame);
 }
 
 void OpenedFrameTracker::remove(WebFrame* frame) {
   m_openedFrames.erase(frame);
 }
 
 void OpenedFrameTracker::transferTo(WebFrame* opener) {
   // Copy the set of opened frames, since changing the owner will mutate this
   // set.
   HashSet<WebFrame*> frames(m_openedFrames);
   for (WebFrame* frame : frames)
     frame->setOpener(opener);
 }
 
-void OpenedFrameTracker::traceFrames(Visitor* visitor) {
-  for (WebFrame* frame : m_openedFrames)
-    WebFrame::traceFrame(visitor, frame);
-}
-
 }  // namespace blink