Complete I/O block GLSL tests The tests meant to perform a draw call and validate the correctness of the shaders. Bug: angleproject:3580 Change-Id: I3a008d204ae3d7dceb731ba7a815ab54f38c2920 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2599938 Reviewed-by: Jonah Ryan-Davis <jonahr@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>