Created Unassigned: Custom Extenders render link which fails with 404 [27930]

We have an assembly with

```
public class VoliaMaskedEditExtender : ExtenderControlBase
```

this extender is added to the page and it renders some __WebResource.axd__ url which returns 404.

We would like to get rid of it so I debugged and found that it is added inside __ExtenderControlBase.OnLoad()__

To be more specific within __ToolkitResourceManager.GetStyleNames()__ always added __Background.min.css__ and it is obviously missing in the custom extender assembly

In order to workaround this issue I had to add an embedded resource __Background.min.css__ into the custom extender assembly.