appendSegmentIndex(segmentIndex) {
    goog.asserts.assert(
        this.indexes_.length == 0 || segmentIndex.getNumEvicted() == 0,
        'Should not append a new segment index with already-evicted segments');
    this.indexes_.push(segmentIndex);
  }
Append a SegmentIndex to this MetaSegmentIndex.  This effectively stitches
the underlying Stream onto the end of the multi-Period Stream represented
by this MetaSegmentIndex.

@param {!shaka.media.SegmentIndex} segmentIndex