ined) {
          subSlice.parentContainer = parentContainer;
        }
      }
    },

    get viewSubGroupTitle() {
      return this.title;
    },

    // Certain AsyncSlices can provide a grouping key to group a set of
    // independent tracks, while grouping by |viewSubGroupTitle| puts slices
    // into a single (maybe multi-row but single) track.
    get viewSubGroupGroupingKey() {
      return undefined;
    },

    get userFriendlyName() {
      return 'Async slice ' + this.title + ' at ' +
      