Fixed the Pyrex implementation of Mark class.
Fixed the Pyrex implementation of Mark class.

fuchsia-mirror/third_party-pyyaml,jamesbroadhead/pyyaml,yaml/pyyaml,anishathalye/pyyaml,yaml/pyyaml,jamesbroadhead/pyyaml,anishathalye/pyyaml,yaml/pyyaml,fuchsia-mirror/third_party-pyyaml