SimpleMessageBoxViews: UI message loop does not need to be running on Linux.
Fixes ProcessSingletonDialogLinux not showing a dialog.
BUG=367048
TEST=run "mkdir /tmp/locktest && ln -s fakehost-1234 /tmp/locktest/SingletonLock && chrome --user-data-dir=/tmp/locktest". A dialog should appear allowing you to quit or unlock the profile. If you click quit, /tmp/locktest/SingletonLock file should remain untouched. If you click unlock, chrome should launch normally.
Review URL: https://codereview.chromium.org/
261753015
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@268793 0039d316-1c4b-4281-b951-d872f2087c98