have snapshots of the same histogram,
 * the snapshots will be merged.
 */
tr.exportTo('tr.metrics', function() {
  function parseBuckets_(event, processName) {
    const len = tr.b.Base64.getDecodedBufferLength(event.args.buckets);
    const buffer = new ArrayBuffer(len);
    const dataView = new DataView(buffer);
    tr.b.Base64.DecodeToTypedArray(event.args.buckets, dataView);
    // Negative numbers are not supported, for now.
    const decoded = new Uint32Array(buffer);
    const sum = decoded[1] + dec