Add separate import for `IsolateChannel` (dart-lang/stream_channel#40)

This will allow us to move to this import in the few packages which are
using this class, like test, without having a fully broken state in
between, and without required `git` dependency overrides.
4 files changed
tree: 94eca96d9444a271b5bf07bd9d7440d326d9be4d
  1. pkgs/