Updated Image9 to use gl::Errors for staging texture manipulation. BUG=angle:520 Change-Id: I527a2bcadbf1abb05bd461d35ddbd7e28d487639 Reviewed-on: https://chromium-review.googlesource.com/221396 Reviewed-by: Brandon Jones <bajones@chromium.org> Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>