So I wanted to set an Id dynamically in dart, but i can't access it. `btn` will always be null. Chrome does show that the Button got the Id, but i get no Access to the Id in Dart..

```
    // extended Td html
    <polymer-element 
        name="crud-tr" extends="tr" attributes="metaData entry">   
        <script type="application/dart" src="crud-tr.dart"></script> 
    </polymer-element>

```

--

```
// extended Td Dart
@CustomTag('crud-tr')
class CrudTrElement extends TableRowElement with Polymer, Observable {
    void attached() {
        super.attached();
        TableCellElement editTd = new TableCellElement();      
        ButtonElement edit_cancel = new ButtonElement();
        edit_cancel
            ..text = "Edit"
            ..id = 'edit_cancel'
            ..onClick.listen((event) => toggleEditMode());
        editTd.append(edit_cancel);

        TableCellElement deleteTd = new TableCellElement(); 
        ButtonElement delete_save = new ButtonElement();
        delete_save
            ..id = 'delete_save'
            ..text = "Delete"
            ..onClick.listen((event) => deleteEntry());
        deleteTd.append(delete_save); 

        this
            ..append(editTd)
            ..append(deleteTd);
    }

    void toggleEditMode() {         
            ButtonElement editBtn = this.shadowRoot.querySelector('#edit_cancel');
            ButtonElement deleteBtn = this.shadowRoot.querySelector('#delete_save');
            /* -> Both null / Exception */      
    }

     CrudTrElement.created() : super.created() {
        polymerCreated();
    }
}         

```