Detach old frame on WebFrame::swap.

Source/core/loader/FrameLoader.h

Index: Source/core/loader/FrameLoader.h
diff --git a/Source/core/loader/FrameLoader.h b/Source/core/loader/FrameLoader.h
index 3bf958ac3c9b9432fec255e12a160d7b292a6734..7c5aa54533ea2d1bcf465c11d659565222de465f 100644
--- a/Source/core/loader/FrameLoader.h
+++ b/Source/core/loader/FrameLoader.h
@@ -152,6 +152,11 @@ public:
     void finishedParsing();
     void checkCompleted();
 
+    // This prepares the FrameLoader for the next commit. It will dispatch
+    // unload events, abort XHR requests and detach the document. Returns true
+    // if the frame is ready to receive the next commit, or false otherwise.
+    bool prepareForCommit();
+
     void commitProvisionalLoad();
 
     FrameLoaderStateMachine* stateMachine() const { return &m_stateMachine; }