It makes sure the resulting options.reviewers and options.cc are internally
consistent by splitting comma separated items.

R=iannucci@chromium.org
BUG=


Review URL: https://chromiumcodereview.appspot.com/13843002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@193496 0039d316-1c4b-4281-b951-d872f2087c98