For new users wanting to try Dart out that don't have SDK in PATH the experience is a bit lame (the extension won't even activate). It would be nice if we could offer to download the SDK (either ask them for a path, or if we have a kind of persisted-temp folder we can write to, then we can progamatically set the sdkPath setting) and use for Analyzer and running command line apps.

This would be especially useful on Windows where Dart has no official installer and manual install involves adding to PATH manually, etc.

The complicated parts are probably:

• Getting the correct SDK (Mac/Linux/Windows/x64/x86)
• A reliable unzip that works on all platforms