Adds a new blocklist feature WEBRENDER_ANGLE_METAL which determines
whether we are allowed to run webrender on ANGLE's Metal backend on
macOS. The existing WEBRENDER_ANGLE gfxFeature now depends on either
D3D11_HW_ANGLE or WEBRENDER_METAL_ANGLE, on Windows and macOS
respectively.
WEBRENDER_ANGLE_METAL is currently universally blocked, as we don't yet
build or ship the required ANGLE libraries on macOS. There are also
specific blocks for macOS versions earlier than 12, and for devices with
mutliple GPUs, as they will require additional work to unblock following
the initial rollout.
Lastly, universally set the UseWebRenderANGLE gfxVar based on the
WEBRENDER_ANGLE gfxFeature status. This ensures the gfxVar will be set
true on macOS once the required blocklist and prefs are enabled. On
platforms without an ANGLE backend feature the WEBRENDER_ANGLE feature
will always be disabled anyway.
Differential Revision: https://phabricator.services.mozilla.com/D311497
Jamie Nicol
b431c75012