HTML5 Video: fix a crash issue that when browser plays H.264 in fullscreen and goes to background.
HTML5 Video: fix a crash issue that when browser plays H.264 in fullscreen
and goes to background.

The root cause is post the exit direct rendering IPC message in a thread
other than render thread.

This patch is from Xuefeng Deng. Reviewed by Ningxin

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser