Use the specified Program instead of current in GetUniform. This bug slipped in with the GetUniform validation refactor. BUG=angle:571 Change-Id: I2b87e6fe98224ba99c5b21a71d66b197fd618741 Reviewed-on: https://chromium-review.googlesource.com/214872 Reviewed-by: Nicolas Capens <capn@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>