code: function loadTheme(id) {
          var extension = extensions[id];
          if (extension.installInfo && extension.installInfo.metadata && extension.installInfo.metadata.theme) {
              ThemeManager.loadPackage(extension.installInfo);
          }
      }
docs: @private
  Verifies if an extension is a theme based on the presence of the field "theme"
  in the package.json.  If it is a theme, then the theme file is just loaded by the
  ThemeManager
  
  @param {string} id of the theme extension to load