Fix a threading bug in the brlapi basec braille controller
This CL enables brlapi support by default in builds for chromeos (it's already enabled by default in chromeos itself, so that part is a noop). This revealed a threading bug in the implementation which is also fixed my moving a file_path_watcher from the IO thread to the FILE threadd.
BUG=178559
Review URL: https://chromiumcodereview.appspot.com/
24325002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225008 0039d316-1c4b-4281-b951-d872f2087c98