We keep the XBL binding around for <content>, <constructor>, and <destructor>. This can
eventually be migrated to a Custom Element once we have platform support, but in the meantime
this is a way to get the many thousands of LOC into a JS class.
MozReview-Commit-ID: 1dCQp527yF9
This will allow us to preserve blame as best as possible when the implementation
of this binding gets rewritten to JS in the next changeset.
MozReview-Commit-ID: HTBXcvQDAQZ