5382e56f05
Introduce an ast node for explicit 'assignable to' type checks. Remove Instance::Is() helper. Review URL: http://codereview.chromium.org//8678031 git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@1827 260f80e4-7a28-3924-810f-c04153c831b5