Enable prefer_typing_unitialized_varables lint (dart-lang/stream_channel#30)

Work towards dart-lang/stream_channel#29

Using the lint catches a bug were an uninitialized variable was causing
an instantiation to pick up a reified type of `dynamic` instead of a
useful type.
11 files changed
tree: 0f7fb7138d608f21f0e299db2e8edcfa89a88cb3
  1. pkgs/