Also going to toss out there that we now have 
LayerTreeHost::ReleaseLayerTreeFrameSink() aka Compositor::ReleaseAcceleratedWidget() which is relatively new. If the VizProcessFactory hears about the context loss it could retrieve the LayerTreeFrameSinks from cc by calling that, and cc wouldn't need any other signals.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b311d7bf3bc03d9706c0d43624afdb56a7978610

commit b311d7bf3bc03d9706c0d43624afdb56a7978610
Author: kylechar <kylechar@chromium.org>
Date: Thu Oct 26 01:16:47 2017

viz: Use one ContextProvider for all ui::Compositors.

The ui::Compositor doesn't share a ContextProvider with the viz::Display
when running with --enable-viz. All ui::Compositors can use the same
ContextProvider as a result.

Bug:  776052 ,  770833 
Change-Id: I4c5df37ce73d4aefbbb6991f027103635cb15729
Reviewed-on: https://chromium-review.googlesource.com/736331
Commit-Queue: kylechar <kylechar@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#511680}
[modify] https://crrev.com/b311d7bf3bc03d9706c0d43624afdb56a7978610/content/browser/compositor/viz_process_transport_factory.cc
[modify] https://crrev.com/b311d7bf3bc03d9706c0d43624afdb56a7978610/content/browser/compositor/viz_process_transport_factory.h

This is fixed for --enable-viz. It's possible to get MusContextFactory to do something similar, but MusContextFactory is used but all mus clients so there would need to be some way to switch the behaviour on or off per client.

Migrating from Internals>Viz to Internals>Services>Viz.