Incremental compiler: support optional arguments.

R=johnniwinther@google.com

Review URL: https://codereview.chromium.org//740273003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42235 260f80e4-7a28-3924-810f-c04153c831b5
Fix crash in typechecker

BUG=http://dartbug.com/21793
R=floitsch@google.com

Review URL: https://codereview.chromium.org//787753005

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42236 260f80e4-7a28-3924-810f-c04153c831b5
Revert revision 42225 "Simplify subscriptions updating implementation."

This is causing null pointer exceptions in editor testing, see e.g.
http://build.chromium.org/p/client.dart/builders/dart-editor-mac-be/builds/12190/steps/run_tests/logs/stdio

Review URL: https://codereview.chromium.org//790083003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42237 260f80e4-7a28-3924-810f-c04153c831b5
Generate typedef node from the element.

BUG=
R=sigurdm@google.com

Review URL: https://codereview.chromium.org//764023005

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42238 260f80e4-7a28-3924-810f-c04153c831b5