Currently using standard Google Closure Library defines is a bit finicky due to requiring the user to remember that tests must be hinted (otherwise a _truth test is emitted, defeating tree shaking). Given that we have extern processing we could trivially extract type information for the required Google Closure library and allow users to skip the hint.
A first pass would be just to make this work for goog.** namespaces, later we can consider Closure compatible libraries.
