Output the subkey type for list policies on the plist generator.

BUG=61734
R=pastarmovj@chromium.org

Review URL: https://codereview.chromium.org/138343003

git-svn-id: http://grit-i18n.googlecode.com/svn/trunk@146 7262f16d-afe8-6277-6482-052fa10e57b1