Oops, I don't think I meant to commit that. That switches the test harness over from running the Dart code to running the compiled JS.

Essentially, for the Dart version to run, you have to de-symlink the test/app/packages directory. And for the JS one to run, you have to switch the html file over and remember to re-compile the dart code after each change.

I'll revert this, although if we want to switch the test apps over to using the compiled JS output, that works for me.