Added an egl::Error class and updated libEGL to use it. BUG=angle:520 Change-Id: I792c8ddd8e8b76184f566294196d089bc9d1902a Reviewed-on: https://chromium-review.googlesource.com/223270 Reviewed-by: Brandon Jones <bajones@chromium.org> Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>