Improve geolocation permission request tests

[Chris Coulson]

The geolocation permission request test loads a document that tries to use navigator.geolocation, and tests the response to accepting, denying and ignoring the request. It also verifies that a pending request is cancelled by Oxide (indicating to the application that the request should be hidden) when the top level document is navigated.

However:

- We don't test subframe requests.
- We don't verify that pending requests for subframes are cancelled if the frames are navigated or deleted.
- We should verify that pending requests are cancelled at the correct time (which is currently when a new document is committed)