Migrating Tomcat 7 to Tomcat 8 API

I have a library (not of my own authorship) that is integrated with the Tomcat 7 API. The migration guide says in general terms that it is widely compatible and suggests looking at the javadocs, but this is a little vague, especially for someone. not too familiar with Tomcat internal APIs. Can anyone point out a better migration documentation?

Concrete example: the org.apache.naming.resources.WARDirContext class is missing, what replaces it in the new structure?