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

Source/WebKit/chromium/public/WebFrameClient.h

 /*
  * Copyright (C) 2011, 2012 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 206 matching lines @@
 
     // The page title is available.
     virtual void didReceiveTitle(WebFrame* frame, const WebString& title, WebTextDirection direction) { }
 
     // The icon for the page have changed.
     virtual void didChangeIcon(WebFrame*, WebIconURL::Type) { }
 
     // The frame's document finished loading.
     virtual void didFinishDocumentLoad(WebFrame*) { }
 
+    // The 'load' event is about to be dispatched.
+    virtual void willHandleOnloadEvents(WebFrame*) { }
+
     // The 'load' event was dispatched.
     virtual void didHandleOnloadEvents(WebFrame*) { }
 
     // The frame's document or one of its subresources failed to load.
     virtual void didFailLoad(WebFrame*, const WebURLError&) { }
 
     // The frame's document and all of its subresources succeeded to load.
     virtual void didFinishLoad(WebFrame*) { }
 
     // The navigation resulted in no change to the documents within the page.
@@ skipping 202 matching lines @@
     // Extensions3D.h in WebCore/platform/graphics).
     virtual void didLoseWebGLContext(WebFrame*, int) { }
 
 protected:
     ~WebFrameClient() { }
 };
 
 } // namespace WebKit
 
 #endif