Fix comparing TextureFunction structures. Test each field for smaller or larger than, and when they're equal test the next field. BUG=angle:605 Change-Id: I2c5a90d95c7ff73b83f3067381c14b74a213ef05 Reviewed-on: https://chromium-review.googlesource.com/194602 Tested-by: Nicolas Capens <nicolascapens@chromium.org> Reviewed-by: Shannon Woods <shannonwoods@chromium.org>