Platform interfaces for Bluetooth testing

In order to support Mozilla's upcoming implementation of Web Bluetooth,
we're looking at publishing Chromium's Web Bluetooth tests and the platform
interfaces they use.
https://github.com/WebBluetoothCG/web-bluetooth/pull/157 has a first cut at
specifying the platform interfaces we're currently using. We'd welcome
feedback on the names and structure, in order to make the tests as useful
as possible to other implementers.

Domenic mentioned using WebDriver for some of this, but I'm having trouble
finding WebDriver uses in Blink, so that may not be an option for our
implementation.

Thanks,
Jeffrey