Add dart analyzer

Seems working. https://github.com/ajaxorg/ace/issues/2176

Can anybody help to improve my code?
I created and compiled to js the main file:
```
main(List<String> args) {
  var src = args[0];
  var exports = args[1];
  // ... run parser, fill errorListener.errors
  exports.errors = errorListener.errors;
}
```
Then, I wrapped the code with define(..) and added the chunk:
```javascript
var main;
function dartMainRunner(fn) {
    main = fn;
}

var errorList = {
    set$errors : function(errors) {
        this.errors = errors;
    }
};

exports.run = function(src) {
    main([src, errorList]);
    return errorList.errors;
};
```
Can we make it better?