Currently, "CreateDisplayCompositor" is part of the GpuServiceInternal interface. This causes all kinds of problems including a recent tear down deadlock/crash that I have addressed for the short term here: https://codereview.chromium.org/2525213002/

GpuServiceInternal largely lives on the gpu thread, and DisplayCompositor lives on the compositor thread.

In Jellyfish, we had a DisplayCompositorFactory interface that the display compositor host requested and then called "CreateDisplayCompositor" on that interface. We can do the same here. This would allow us to decouple from GpuServiceInternal and make tear down simpler.

Here's the jellyfish impl: https://github.com/danakj/chromium/blob/jellyfish/cc/service/display_compositor_factory.h

Here's the interface:

https://github.com/danakj/chromium/blob/jellyfish/cc/ipc/compositor.mojom