Isolates: allow sending of arbitrary objects in dart2js.

BUG= http://dartbug.com/12628
BUG= http://dartbug.com/9245
R=lrn@google.com, sigurdm@google.com, sra@google.com

Review URL: https://codereview.chromium.org//742873002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42161 260f80e4-7a28-3924-810f-c04153c831b5
Improve receiver narrowing in type propagation.

BUG=
R=johnniwinther@google.com

Review URL: https://codereview.chromium.org//771613002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42162 260f80e4-7a28-3924-810f-c04153c831b5
Update status file.

Review URL: https://codereview.chromium.org//785963002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42163 260f80e4-7a28-3924-810f-c04153c831b5