It would be nice if the main driver (this file) could allow specifying where to find 'wrk' like it does for d8. Also, it might be nice to just skip the I/O tests if wrk isn't found -- and maybe we should do the same if we can't find d8.

   Running DeltaBlue:
      Dart       : .... runs/sec
      Dart2JS : Skipped (set path to JS runner using -DJS=...)
      JS          : Skipped
   ...
   Running Hello:
      Dart      : Skipped (set path to WRK tool using -DWRK=...)