Update cmake
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Webxr magicleap
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Adds the magicleap back end for webxr.
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Remove most of the things in layout 2020
We keep mostly the query system. There is probably more to delete but
that's a good start I think.
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Do not start up webvr services when running webxr and vice versa
Once we move everything over to the webxr crate we can relax the restriction around running both webxr and webvr
r? @asajeffrey
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Remove GStreamer dependencies from UWP app.
Remove all GStreamer dependencies and restore MSVC CRT dependencies to allow running the UWP on non-desktop devices.
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It's impossible to conditionally use a crate based only on cargo features, so
temporarily disable the backend on all Windows builds while we sort out how
to get the UWP builds working again.
WebXr: allow for only a single raf message, until callbacks execute
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See https://github.com/servo/webxr/issues/34
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