Make SkSurface_Base::type() and onCapabilities() pure virtual Change-Id: Icbbea08bd0a4bfa52e961984eff0a274814da92b Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1221836 Reviewed-by: Kaylee Lubick <kjlubick@google.com> Commit-Queue: Jorge Betancourt <jmbetancourt@google.com>