Fix a race condition where rapid back/forward clicks could close a tab...

chrome/browser/browser.cc

Index: chrome/browser/browser.cc
===================================================================
--- chrome/browser/browser.cc	(revision 21465)
+++ chrome/browser/browser.cc	(working copy)
@@ -2487,7 +2487,7 @@
     // Null check render_view_host here as this gets called on a PostTask and
     // the tab's render_view_host may have been nulled out.
     if (tab->render_view_host()) {
-      tab->render_view_host()->FirePageUnload();
+      tab->render_view_host()->ClosePage(false, -1, -1);
     } else {
       ClearUnloadState(tab);
     }