This shader previously output red and green in a checkered pattern (with
four regions).  This makes it hard to verify that the output is not
rotated / flipped.

This change makes the shader output:

    +--------+--------+
    |  red   |  blue  |
    +--------+--------+
    | green  | yellow |
    +--------+--------+

Bug: angleproject:4901
Change-Id: I02723306dec17d1419f11d9f76e96b1cefc3bf06
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2498261Reviewed-by: Ian Elliott <ianelliott@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>