Fix a bug in instance canonicalization and add debug mode checks that we are not missing any fields.

R=asiva@google.com

Review URL: https://codereview.chromium.org//17104002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@24059 260f80e4-7a28-3924-810f-c04153c831b5
2 files changed