Add cube map to read-outside-framebuffer tests. Cube maps go through a separate path on D3D so we need to test them. BUG=angleproject:1815 Change-Id: Ifb7a85d7e2750f25bce382fdd7a00062d23b3573 Reviewed-on: https://chromium-review.googlesource.com/597213 Commit-Queue: Frank Henigman <fjhenigman@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>