function addPluginCategory(sampleLhr) {
  sampleLhr.categories['lighthouse-plugin-someplugin'] = {
    id: 'lighthouse-plugin-someplugin',
    title: 'Plugin',
    score: 0.5,
    auditRefs: [],
  };
}
Add a plugin to demo plugin rendering.
@param {LH.Result} sampleLhr