glCopyTexSubImage2d and glReadPixels should generate a
GL_INVALID_OPERATION when GL_NONE is specified as a color buffer.
There are two tests added which cover glCopyTexSubImage2D and
glReadPixels.
BUG=angleproject:1445
TEST=angle_end2end_tests
Change-Id: I3ab1428aad7eee96ca2330909e2b6f765f539705
Reviewed-on: https://chromium-review.googlesource.com/360860Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
