ANGLE_USE_OZONE is not defined in tests, but USE_OZONE is so use the latter.

BUG=angleproject:1423

Change-Id: Ib758fec6a1bb8d5cc66d0994cba2142e6a7f82b0
Reviewed-on: https://chromium-review.googlesource.com/474113
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>