Extend timing buffer in audit test (dart-lang/stream_transform#154)

This test relies on the particular interleaving of creating one `Timer`
and two `Future.delayed`. The 5 millisecond timer must fire after the
first 3 millisecond delay, and before the subsequent 3 millisecond
delay. On the web this timing became unreliable - the `Timer` may not
fire until after the full 6 milliseconds of both delays.

Extend the delays to 6 for the `Timer`, and 4 + 4 for the
`Future.delayed`. The extra millisecond of padding improves behavior on
the web.
1 file changed
tree: 773a421b1b71071e69b72e1e1d284460e3997ec7
  1. pkgs/