servo: Merge #17068 - Separate waking the event loop, from communicating with...

servo: Merge #17068 - Separate waking the event loop, from communicating with Compositor (from gterzian:remove_compositorproxy); r=asajeffrey

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@paulrouget first step of #15934, Glutin only for now, please take a look...

If this makes sense, I will also update the code for ports other than Glutin...

One question: one do I add the `warn!` macro to `servolib`? Also perhaps we would also want to add `box`, since I had to switch to using `Box::new`...

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Source-Repo: https://github.com/servo/servo
Source-Revision: 7e273d6c9b86d6ffbf216e84ae7326976888e5ef

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 89118c463da42f53cd2d9df0c97121f71d81600f