code: function getCategoriesInfo(serviceRegistry) {
  		// Read categories.
  		var categoryInfos;
  		if (!_cachedCategories) {
  			categoryInfos = [];
  			var navLinkCategories = serviceRegistry.getServiceReferences("orion.page.link.category"); //$NON-NLS-0$
  			navLinkCategories.forEach(function(serviceRef) {
  				var info = _getPropertiesMap(serviceRef);
  				if (!info.id || (!info.name && !info.nameKey)) {
  					return;
  				}
  				info.service = serviceRegistry.getService(serviceRef);
  				info.textContent = info.name;
  				categoryInfos.push(new Deferred().resolve(info));				
  			});
  			return Deferred.all(categoryInfos).then(function(infos) {
  				_cachedCategories = new CategoriesInfo(infos);
  				return _cachedCategories;
  			});
  		}
  		return new Deferred().resolve(_cachedCategories);
  	}
docs: Reads info about page link categories.
  @returns {orion.Promise} Resolving to {@link orion.PageLinks.CategoriesInfo}