Bump stream_channel and watcher
Bump stream_channel and watcher

Change-Id: I643a4237fb65b04780d7a8d6408adca2e0e8cedd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/168740
Reviewed-by: Kevin Moore <1d6e7d10d051cf619c5282da3c28fd8d3e0a65a4@google.com>
Commit-Queue: Samuel Rawlins <5cf2cac5eec2ad6d0eb2b0f4ff6af9a590ce2bf6@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk