docs: function(type, handler) {
        if (!this.listeners_)
          return;
        if (type in this.listeners_) {
          var handlers = this.listeners_[type];
          var index = handlers.indexOf(handler);
          if (index >= 0) {
            // Clean up if this was the last listener.
            if (handlers.length == 1)
              delete this.listeners_[type];
            else
              handlers.splice(index, 1);
          }
        }
      }