Load a dart script dynamically using dart

I'm trying to load a dart script dynamically using dart. I'm using something like this:

test.html:

...
<script src="http://dart.googlecode.com/svn/branches/bleeding_edge/dart/client/dart.js"></script>
<script type="application/dart" src="test.dart"></script>
...

test.dart:

#import('dart:html');
main() {
    var script = new ScriptElement();
    script.type = 'application/dart';
    script.src = 'helloworld.dart';
    document.body.elements.add(script);
}

It doesn't work. However, if I inline the same code in the HTML file, it works fine:

test.html:

...
<script src="http://dart.googlecode.com/svn/branches/bleeding_edge/dart/client/dart.js"></script>
<script type="application/dart">
#import('dart:html');
main() {
    var script = new ScriptElement();
    script.type = 'application/dart';
    script.src = 'helloworld.dart';
    document.body.elements.add(script);
}
</script>
...

Why is this happening?