Oilpan: extend tracing over WebFrame trees.

Source/web/OpenedFrameTracker.h

Index: Source/web/OpenedFrameTracker.h
diff --git a/Source/web/OpenedFrameTracker.h b/Source/web/OpenedFrameTracker.h
index d17e0f73bb3b7d898222f14c29b868e061faaa48..653654271849d2af902fb083e1e7b4af753ac48d 100644
--- a/Source/web/OpenedFrameTracker.h
+++ b/Source/web/OpenedFrameTracker.h
@@ -10,6 +10,7 @@
 
 namespace blink {
 
+class Visitor;
 class WebFrame;
 
 // Small helper class to track the set of frames that a WebFrame has opened.
@@ -28,6 +29,8 @@ public:
     // Updates the opener for all tracked frames.
     void updateOpener(WebFrame*);
 
+    void traceFrames(Visitor*);
+
 private:
     WTF::HashSet<WebFrame*> m_openedFrames;
 };