Add missing signatures for add and addAll to priority queue.
Add missing signatures for add and addAll to priority queue.

R=ajohnsen@google.com

Review URL: https://codereview.chromium.org//121583004

git-svn-id: 14b45b9c3b6048558bb8b0fd3dfaa8c11e412a81@31541 260f80e4-7a28-3924-810f-c04153c831b5

dart-lang/collection