These were causing validation errors in the dEQP FBO tests.
See Table 3.2 in the ES3 spec.

BUG=angleproject:1074
TEST=dEQP-GLES3.functional.fbo.completeness.renderable.texture.color0.*

Change-Id: Ifbf9199c54060eb3fc1a1dac7bbd74e19e013c61
Reviewed-on: https://chromium-review.googlesource.com/286773Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>