Clear opener when frame is detached.

third_party/WebKit/Source/web/OpenedFrameTracker.cpp

Index: third_party/WebKit/Source/web/OpenedFrameTracker.cpp
diff --git a/third_party/WebKit/Source/web/OpenedFrameTracker.cpp b/third_party/WebKit/Source/web/OpenedFrameTracker.cpp
index cc96b6440528143a05845bd3935c15318213a4e7..72d3e2e3edec2ac4ac9ace25bc012188245694f2 100644
--- a/third_party/WebKit/Source/web/OpenedFrameTracker.cpp
+++ b/third_party/WebKit/Source/web/OpenedFrameTracker.cpp
@@ -33,9 +33,4 @@ void OpenedFrameTracker::transferTo(WebFrame* opener) {
     frame->setOpener(opener);
 }
 
-void OpenedFrameTracker::traceFrames(Visitor* visitor) {
-  for (WebFrame* frame : m_openedFrames)
-    WebFrame::traceFrame(visitor, frame);
-}
-
 }  // namespace blink