rebaseline_server: add urlSchemaVersion parameter

In https://codereview.chromium.org/369473005 ('rebaseline_server: handle category filtering more generically'), I am changing the meaning of some URL parameters.  If a user pastes an old URL into an updated rebaseline_server instance, they may get unexpected results.  Adding a urlSchemaVersion parameter allows us to automatically convert the URL, or at least warn the user.

BUG=skia:2230
NOTRY=True
R=jcgregorio@google.com

Author: epoger@google.com

Review URL: https://codereview.chromium.org/368933002
4 files changed