Intent to ship: WebVR on macOS

[Kearwood Kip Gilbert]

As of 2017-10-01, I intend to turn WebVR on by default for macOS. It has been developed behind the dom.vr.enabled preference. We have already shipped WebVR by default for the Windows platform. macOS support has been implemented for several months but disabled by default. Our WebVR implementation supports OpenVR for the HTC Vive on macOS High Sierra, which is now hitting release.
This feature was previously discussed in this "intent to implement" thread: <https://groups.google.com/forum/#!forum/mozilla.dev.platform>.
Bug to turn on by default: https://bugzilla.mozilla.org/show_bug.cgi?id=1374399
Link to standard: https://w3c.github.io/webvr/spec/1.1/
Testing:
Automated tests have been implemented and are already active for the macOS builds in taskcluster. Platform conformance tests are shared with other UA’s.

[kear...@kearwood.com]

As of 2018-02-27, I intend to turn WebVR [back] on by default for macOS. Due to hardware availability for QA, this was disabled before riding to release for FF58 and FF59. We have since gained QA approval to allow it to ride to release in FF60.

Bug to turn on by default:

https://bugzilla.mozilla.org/show_bug.cgi?id=1438044

[kgil...@mozilla.com]

Enabling this was delayed / rolled back due to issues with the SteamVR runtime on macOS occurring when we disabled the macOS nano-allocator for the Firefox process to fix unrelated issues. Updates to the SteamVR runtime have corrected this.

This will be re-re-enabled for FF64 on 2018-10-12. The new bug to turn on by default:

Bug 1476091 ((Re-) Enable WebVR by default for macOS)