Removed a lot of warnings and hints when opening many pkg projects in the editor

R=gram@google.com

Review URL: https://codereview.chromium.org//22284003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/mime@25831 260f80e4-7a28-3924-810f-c04153c831b5