Support comma separated hardware keyboard layout in ChromeOS OOBE UI.

BUG=344340
TEST=manual

Review URL: https://codereview.chromium.org/169683002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251686 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251686