This moves the GL accelerated media setup out of `RenderingContext`
which prevents making libservo dependo on the Wayland and X11 versions
of surfman explicitly. This support is experimental and (honestly) a bit
broken. I've confirmed that this works as well as it did before the
change.
The main thing here is that the configuration, which currently needs
surfman types, moves to servoshell. In addition:
1. Instead of passing the information to the Constellation, the setup is
stored statically. This is necessary to avoid introducing a
dependency on `media` in `webrender_traits`. It's quite likely that
`media` types should move to the internal embedding API to avoid
this. This is preserved for a followup change.
2. The whole system of wrapping the media channels in an abstract type
is removed. They could be either mpsc channels or IPC channels. This
was never going to work because mpsc channels cannot be serialized
and deserialized with serde. Instead this just uses IPC channels. We
also have other ways of doing this kind of abstraction in Servo so we
do not need another. The `mpsc` version was hard-coded to be
disabled.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
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