Remove a few warnings by adding down-casting assingments.
Remove a few warnings by adding down-casting assingments.

Also reformat the source.

BUG=
R=eernst@google.com

Review URL: https://codereview.chromium.org/1269323002 .

google/reflectable.dart,luisvt/reflectable,google/reflectable.dart,luisvt/reflectable