Add 'Hide content' button in QUnit toolbar

Hi!
I have a 11-inch laptop and if i open chrome dev tools I don't can see part of results of tests.
It looks like this:

![screenshot]
(https://www.evernote.com/shard/s424/sh/695ac905-d54b-4975-8a58-9ad665bdfa1a/a26c38281025bfc1a903c0678144dee7/deep/0/--Apollo-Tests-and-test-helper.js---apollo.png)

It would be great able to toggle the visibility of the test container.