Finding which libraries/packages won't compile.

These will not compile under dart2js:
  dart:io
  dart:http
  package:analyzer (relies on dart:io)
  package:barback (relies on dart:io)
  package:http (relies on dart:io)
  package:oauth2 (relies on package:http/src/* which rely on dart:io)
  package:scheduled_test (relies on dart:io)
  package:watcher (relies on dart:io)
pub.dart compiling with stubs for io.dart.

Now pub.dart is compiling (at least the files needed for 'pub get').
The tests are not though, as 'package:scheduled_test' is not able to
be compiled to JS. All directory/files currently ignored are prefixed
by '_'.