Cannot resolve plugin 'Dart' in dependencies

I am beginning work on a plugin where I will need the Dart plugin as a dependency.  From what I have read and from looking at examples, I have added <depends>Dart</depends> in my plugin.xml.  But I get error Cannot resolve plugin 'Dart' in dependencies.  I'm assuming I'm missing something, but for the life of me I can't figure out where it is.  Any insight would be appreciated.