Ignore JavaScript messages (alert/confirm/prompt) during unload handlers.

content/browser/tab_contents/background_contents.h

Index: content/browser/tab_contents/background_contents.h
diff --git a/content/browser/tab_contents/background_contents.h b/content/browser/tab_contents/background_contents.h
index e4455fb39a11bc914280bac1ab7b070158422764..5451203d981e7608eed6dfff699134adc00c7e1e 100644
--- a/content/browser/tab_contents/background_contents.h
+++ b/content/browser/tab_contents/background_contents.h
@@ -72,6 +72,7 @@ class BackgroundContents : public RenderViewHostDelegate,
                                     const std::wstring& default_prompt,
                                     const GURL& frame_url,
                                     const int flags,
+                                    const bool unload_handler_being_run,
                                     IPC::Message* reply_msg,
                                     bool* did_suppress_message);
   virtual void Close(RenderViewHost* render_view_host);