This plugin is built with Buck. Clone or link this plugin to the plugins directory of the Gerrit tree and issue the command:
buck build plugins/javamelody:javamelody
The output is created in
buck-out/gen/plugins/javamelody/javamelody.jar
This project can be imported into the Eclipse IDE:
./tools/eclipse/project.py
More information about Buck can be found in the Gerrit documentation.