Give chromevox access to the commandLinePrivate API on chromeos.

BUG=225886
R=zelidrag@chromium.org

Review URL: https://codereview.chromium.org/130503010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245642 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245642