Bug 712130 - Defer autofocus until after frame construction. r=bz

The autofocus attribute on form elements forces layout in CheckIfFocusable.
To avoid unpleasant FOUCs, defer autofocus processing until frames are
constructed in PresShell::Initialize.

Resolve the race between nsAutoFocusEvent running and page load by checking the
readystate at time of event posting. Skip autofocus if the element moved to a
different window in the meantime.

MozReview-Commit-ID: 90jiJYJWmRg

layout/base/PresShell.cpp

@@ -1817,6 +1817,8 @@ PresShell::Initialize(nscoord aWidth, nscoord aHeight)
     NS_ENSURE_STATE(!mHaveShutDown);
   }
 
+  mDocument->TriggerAutoFocus();
+
   NS_ASSERTION(rootFrame, "How did that happen?");
 
   // Note: when the frame was created above it had the NS_FRAME_IS_DIRTY bit