code: function getProviderIDsForLanguage(languageId) {
          if (!_providers[languageId]) {
              return [];
          }
          return _providers[languageId].map(function (provider) {
              return provider.name;
          });
      }
docs: Returns an array of the IDs of providers registered for a specific language
  
  @param {!string} languageId
  @return {Array.<string>} Names of registered providers.