Is it possible to load a local file into an iframe using file protocol in karma?

### Expected behaviour

Be able to create an iframe in the karma browser and then set the src attribute of the iframe to a local file with the file protocal.

### Actual behaviour

Does not load anything or does not throw any kind of error for loading.

### Environment Details

- Karma version (output of `karma --version`):
- Relevant part of your `karma.config.js` file

karma version 1.3.0

### Steps to reproduce the behaviour

1. Currently this is a question if this is something possible, or limitation to karma.
2. I will create a sample project for this, if needed for further investigation

Start by reproducing the iframe behavior described for Karma 1.3.0, using a browser test that sets an iframe source to a local file with the file protocol. Review the relevant karma.config.js settings and determine whether the behavior is a limitation or a defect; done should include a clear conclusion backed by a reproducible sample or documented limitation.

Written by the indexing model from the issue text.