Adding the extensions datatype to the python sync server.
Adding the extensions datatype to the python sync server.

The sync integration tests run against a local python sync server. The
extensions datatype was recently added to the client code, causing the
python server to require this update.

BUG=48040
TEST=sync_integration_tests

Review URL: http://codereview.chromium.org/2878017

git-svn-id: http://src.chromium.org/svn/trunk/src@51449 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: a30afe6be3ee67ce64953d22abadcecc9641ec44
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser