Added methods to .xml to track users' data usage

BUG=chromium-os:16802
TEST=ran FEATURES=test emerge
Change-Id: Id9d8191bd743fd8b2ba2af8d151900ea3f3b3f05
Reviewed-on: http://gerrit.chromium.org/gerrit/3005
Reviewed-by: Vince Laviano <vlaviano@chromium.org>
Tested-by: Anne Kenyon (Chromium) <annemkenyon@chromium.org>