Plumb an event through to content/ that is sent just before 'onload'.

Source/WebCore/loader/FrameLoader.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) Research In Motion Limited 2009. All rights reserved.
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
@@ skipping 191 matching lines @@
 
     void setDefersLoading(bool);
 
     void didExplicitOpen();
 
     // Callbacks from DocumentWriter
     void didBeginDocument(bool dispatchWindowObjectAvailable);
 
     void receivedFirstData();
 
+    void willHandleOnloadEvents();
     void handledOnloadEvents();
     String userAgent(const KURL&) const;
 
     void dispatchDidClearWindowObjectInWorld(DOMWrapperWorld*);
     void dispatchDidClearWindowObjectsInAllWorlds();
     void dispatchDocumentElementAvailable();
 
     // The following sandbox flags will be forced, regardless of changes to
     // the sandbox attribute of any parent frames.
     void forceSandboxFlags(SandboxFlags flags) { m_forcedSandboxFlags |= flags; }
@@ skipping 236 matching lines @@
 // the frame name references a frame different from the openerFrame, e.g. when it is
 // "_self" or "_parent".
 //
 // FIXME: Consider making this function part of an appropriate class (not FrameLoader)
 // and moving it to a more appropriate location.
 Frame* createWindow(Frame* openerFrame, Frame* lookupFrame, const FrameLoadRequest&, const WindowFeatures&, bool& created);
 
 } // namespace WebCore
 
 #endif // FrameLoader_h