Cast File.openRead() stream to List<int> (#74)
Cast File.openRead() stream to List<int> (#74)

This is in preparation for File.openRead() returning
a `Stream<Uint8List>` rather than `Stream<List<int>>`.
This is a forwards-compatible change that should be
a no-op for existing usages.

dart-lang/sdk#36900
dart-lang/http_io,dart-archive/http_io