[dart:io] Fix ProcessStartMode.values
[dart:io] Fix ProcessStartMode.values

Change-Id: I1bdd98c7e86991e38d6bc7555620d784d595eb2d
Reviewed-on: https://dart-review.googlesource.com/54441
Reviewed-by: Leaf Petersen <9bef692239b5f624cec8e2cd5249ab1939a377aa@google.com>
Commit-Queue: Zach Anderson <9f8b31e960a68dade71618f1ff6da6e23a1edfc9@google.com>

dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk