Fix checked mode errors
Fix checked mode errors

Remove return types from functions which can now return objects of different types.

TBR=ngeoffray@google.com

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com//9816005

git-svn-id: c93d8a2297af3b929165606efe145742a534bc71@5711 260f80e4-7a28-3924-810f-c04153c831b5

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