Updated Image11 to use gl::Errors for staging texture manipulation. BUG=angle:520 Change-Id: I5792b139ddd69c2cabc3b901a7067438c1ee363b Reviewed-on: https://chromium-review.googlesource.com/221395 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>