Chromium and Dart with Dev Tools
There is a public branch of Chromium that embeds the Dart virtual machine, allowing you to run native Dart code directly in the browser. Unfortunately, only the Dartium source is available right now, but if you search hard enough, you might find an enterprisingly fellow providing pre-built binaries (warning: these may blow up your machine.)
Dart is getting ready, please do try it out by learning more, browsing the API, using the Editor, or downloading the SDK. I also have a series of posts on Dart. Please let us know what you think!
The engineers have begun to add Developer Tools support with Dart, which starts to tell the debugging story. With a very recent build of Dartium (2012-01-24) you can try this for yourself. I found breakpoints are working, with a few caveats (eg not working with function callbacks yet.)
To see Chromium + Dart + Dev tools + breakpoints in action:
Dart is getting ready, please do try it out by learning more, browsing the API, using the Editor, or downloading the SDK. I also have a series of posts on Dart. Please let us know what you think!