Separate value parameters from the continuation for symmetry with
function invocations. Do not make closure variables optional. Do not
use '{' or '}', since it makes parsing more difficult and probably
screws up other tools that work with S-expressions.
Move closure variables after the parameters and just before the body,
since they are not part of the signature, do not appear at call sites,
and the implicit box creation happens at the beginning of the body
anyway.
R=asgerf@google.com, karlklose@google.com
BUG=
Review URL: https://codereview.chromium.org//810783002
git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@42395 260f80e4-7a28-3924-810f-c04153c831b5
kmillikin@google.com
09ae999a45