Add IsOzone(). Add a function to check for the Ozone back end for use in skipping tests. BUG=angleproject:1423 Change-Id: Ida3313e8cce5179422bdca85ba68f9765dfac840 Reviewed-on: https://chromium-review.googlesource.com/469068 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Frank Henigman <fjhenigman@chromium.org>