Merge 72590 - [linux] Avoid crash when there's an X error during shutdown.

If X errors after the notification service has been destroyed (during browser shutdown), we'll deref NULL. Instead, we should just ignore the X error (aside from logging it to ERROR).

BUG=70852
TEST=none

Review URL: http://codereview.chromium.org/6379009

TBR=estade@chromium.org
Review URL: http://codereview.chromium.org/6528040

git-svn-id: svn://svn.chromium.org/chrome/branches/648/src@75062 0039d316-1c4b-4281-b951-d872f2087c98