There is no built-in liquibase functions in eclipse. If you are trying to run a Liquibase often from within Eclipse the best option is to use the Ant or Maven interface since they can be easily called from Eclipse commands.
GenerateChangeLog is something you generally only need to run once to bootstrap an existing database into being managed by liquibase, so a quick command line call may be the easiest for you.
The Liquibase Quick Start Guide has an example changelog file for reference as well.