Karma fails when trying to update browser page.

### Expected behavior

Don't fail when manually update browser page.
### Actual behavior

Fails when manually click "Refresh" button (or F5 or CTRL+R) on the "karma tests" page. ("Chrome", "Firefox").
### Enviroment Details
- Windows 7
- Karma version: Karma v1.1.0
- Worked well on the same configuration for Karma v0.13.22
- Relevant part of your `karma.config.js` file:

``` json
{
"singleRun": false,
"autoWatch": true,
"plugins": [
"karma-tap",
"karma-phantomjs-launcher",
"karma-browserify",
"karma-coverage",
"karma-ng-html2js-preprocessor",
"karma-chrome-launcher",
"karma-firefox-launcher"
],
"browsers": ["Chrome", "Firefox", "PhantomJS"],
"frameworks": ["browserify", "tap"]
}
```
### Steps to reproduce the behaviour
1. Run karma with presented configuration
2. Tests would be executed.
3. Go to the Chrome browser
4. Try to update Karma page

Start by reproducing the failure with the shown karma.config.js configuration, then trace how Karma handles a browser page refresh in Chrome and Firefox. Done means manually refreshing the Karma tests page no longer fails while tests continue to execute.

Written by the indexing model from the issue text.