It is triggered by the LessCss compiler in the lesscss-1.7.9.1.1.jar file, META-INF/lessc-rhino-1.7.0.js – it’s an unminified JS file, so it’s simply patched by adding comments before the console.log("done") call.
Also see https://github.com/marceloverdijk/lesscss-java/issues/59