These tests crash the OSX shader compiler. Skip them instead of
expecting a failure.

BUG=angleproject:2137

Change-Id: I4476ba93390ce8dfc1e609e4297d6ce1236d2686
Reviewed-on: https://chromium-review.googlesource.com/671285
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>