linux: set FD_CLOEXEC on the singleton socket
linux: set FD_CLOEXEC on the singleton socket

The IME library may spawn a subprocess, which will then hold open
our singleton socket after we've shut down.

BUG=17952

Review URL: http://codereview.chromium.org/160523

git-svn-id: http://src.chromium.org/svn/trunk/src@22281 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 0581cdcdcfeb6601a33d98a723c09b49cb0ff8c3
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser