Just checking use_ozone fails when building an ozone platform which
doesn't have gbm, e.g. chromecast.

BUG=angleproject:1439
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_gn_chromeos_rel;tryserver.chromium.android:android_compile_dbg

Change-Id: Idec14441ce30dd872b3bfddfe844abfeb910cc02
Reviewed-on: https://chromium-review.googlesource.com/358860Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Frank Henigman <fjhenigman@chromium.org>