Make my pkg packages warning-clean.
Make my pkg packages warning-clean.

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//16097013

git-svn-id: d894903a6691b4329a8535ed724b8f115331b4ef@23620 260f80e4-7a28-3924-810f-c04153c831b5

dart-lang/yaml