k('TraceImport', 'loadTraces');
    const traces = [];
    for (let i = 0; i < filenames.length; i++) {
      traces.push(undefined);
    }
    let numTracesPending = filenames.length;

    filenames.forEach(function(filename, i) {
      getAsync(filename, function(trace) {
        traces[i] = trace;
        numTracesPending--;
        if (numTracesPending === 0) {
          loadTracesMark.end();
          onTracesLoaded(filenames, traces);
        }
      });
    });
  }


  function getAsync(url, cb) {
  