The Dart SDK now has its own repository, joining the numerous Dart tools and packages already in our GitHub org. We’ve moved all the SDK issues over (keeping the original issue numbers!), and dartbug.com now points to GitHub's issue tracker for the Dart SDK.
Getting the SDK source is easy, and we've documented the contribution workflow. Our development tools are optimized for code reviews on Rietveld, Chromium's code review system, and they make it easy to start a review and cleanly land a patch. For very small patches, contributors can use a standard GitHub pull request.
One of the easiest ways to start contributing to Dart is to work on one of our packages. Individual packages (for example, args, http, and test) now have their own repos, complete with their own issue trackers and buildbots. To get started, check them out and find issues marked "help wanted". And of course, we encourage everyone to continue filing issues with dartbug.com.
We hope our move to GitHub helps more Dartisans become active participants in the future of Dart.