[Qt][WebKit2][Mac] WebProcess should exit automatically when UIProcess dies.

[Qt][WebKit2][Mac] WebProcess should exit automatically when UIProcess dies.
https://bugs.webkit.org/show_bug.cgi?id=68439

We use a dispatch queue and a dispatch source in the WebProcess
to receive a notification when the UI Process dies.
The WebProcess then commits suicide.

Patch by Zeno Albisser <zeno.albisser@nokia.com> on 2011-10-03
Reviewed by Andreas Kling.

* WebProcess/qt/WebProcessQt.cpp:
(WebKit::parentProcessDiedCallback):
(WebKit::WebProcess::platformInitializeWebProcess):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@96494 268f45cc-cd09-0410-ab3c-d52691b4dbfc