Adding a bunch of miscellaneous cleanups.

ServerWindowCompositorFrameSink will end up living in mus-gpu, and so it should not have direct access to window server things:

ServerWindowCompositorFrameSink should not refer to ServerWindowCompositorFrameSinkManager (which will go away soonish), and ServerWindow (which lives in mus-ws).

ServerWindowCompositorFrameSink should not refer to anything in services/ui/ws.

FrameGenerator will likely continue to live in the window server, but will be significantly changed in upcoming months. However, this means it cannot refer to ServerWindowCompositorFrameSink directly. Instead, once the root window's CompositorFrameSink is the display CompositorFrameSink, then we should use the same mojo interface that other apps use to add a reference.

Once the split is complete "ServerWindowCompositorFrameSink" becomes a bit of a misnomer. Maybe it can be renamed (yet another rename! YAR! YAR YAR, matey!) to MusCompositorFrameSink!

What are the chances we can use shorter names? :)

Will these frame-sinks be different in salamander with content-frames? If not, how about s/CompositorFrame/Frame/?

Will there be equivalents on the client side? If not, how about s/ServerWindow/Window/?

WindowFrameSink and DisplayFrameSink seems clear enough, and so much shorter than ServerWindowCompositorOnceUponATimeLongAgoFrameSink.

Yes, I suspect we'll have ContentFrameSinks and CompositorFrameSink. We already have WindowCompositorFrameSink in the client lib. ServerWindowCompositorFrameSink is the server-side code.

ServerWindowCompositorFrameSink depends on ServerWindow for two reasons:

1. window()->delegate()->OnScheduleWindowPaint(window()); which is mus' adhoc damage tracking to trigger a new frame. Once Mus uses BeginFrames then this no longer becomes necessary.

2. FrameGenerator::AddOrUpdateSurfaceReference uses it. This can be solved by instead passing in a ServerWindow + CompositorFrameSinkType. Since this is easy to do now, I'll send out a CL shortly.

Once those two are out of the way, then we can introduce a DisplayCompositor::CreateCompositorFrameSink API, and merge DisplayCompositorFrameSink and ServerWindowCompositorFrameSink.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fadcdb0baa1441b4f0ddf1e80e456079b926a357

commit fadcdb0baa1441b4f0ddf1e80e456079b926a357
Author: fsamuel <fsamuel@chromium.org>
Date: Thu Oct 27 22:56:49 2016

Mus: Remove dependency on ServerWindowCompositorFrameSink from FrameGenerator

FrameGenerator will live in mus-ws but ServerWindowCompositorFrameSink
will live in mus-gpu. Thus, we should not access it directly.

ServerWindowCompositorFrameSinkManager now serves as a cache of state
from CompositorFrames submitted to mus-gpu. FrameGenerator looks up
that state in ServerWindowCompositorFrameSink.

BUG= 658988 

Review-Url: https://codereview.chromium.org/2453013002
Cr-Commit-Position: refs/heads/master@{#428182}

[modify] https://crrev.com/fadcdb0baa1441b4f0ddf1e80e456079b926a357/services/ui/ws/frame_generator.cc
[modify] https://crrev.com/fadcdb0baa1441b4f0ddf1e80e456079b926a357/services/ui/ws/frame_generator.h
[modify] https://crrev.com/fadcdb0baa1441b4f0ddf1e80e456079b926a357/services/ui/ws/frame_generator_unittest.cc
[modify] https://crrev.com/fadcdb0baa1441b4f0ddf1e80e456079b926a357/services/ui/ws/server_window_compositor_frame_sink.cc
[modify] https://crrev.com/fadcdb0baa1441b4f0ddf1e80e456079b926a357/services/ui/ws/server_window_compositor_frame_sink.h
[modify] https://crrev.com/fadcdb0baa1441b4f0ddf1e80e456079b926a357/services/ui/ws/server_window_compositor_frame_sink_manager.cc
[modify] https://crrev.com/fadcdb0baa1441b4f0ddf1e80e456079b926a357/services/ui/ws/server_window_compositor_frame_sink_manager.h
[modify] https://crrev.com/fadcdb0baa1441b4f0ddf1e80e456079b926a357/services/ui/ws/server_window_compositor_frame_sink_manager_test_api.cc
[modify] https://crrev.com/fadcdb0baa1441b4f0ddf1e80e456079b926a357/services/ui/ws/window_server.cc
[modify] https://crrev.com/fadcdb0baa1441b4f0ddf1e80e456079b926a357/services/ui/ws/window_server_test_impl.cc
[modify] https://crrev.com/fadcdb0baa1441b4f0ddf1e80e456079b926a357/services/ui/ws/window_tree.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fd24c28f0f2c34d919703c58432f5044bef6b155

commit fd24c28f0f2c34d919703c58432f5044bef6b155
Author: fsamuel <fsamuel@chromium.org>
Date: Wed Nov 02 04:48:18 2016

Mus: Introduce DisplayCompositorClient mojo interface

BUG= 658988 
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel

Review-Url: https://codereview.chromium.org/2449173003
Cr-Commit-Position: refs/heads/master@{#429210}

[modify] https://crrev.com/fd24c28f0f2c34d919703c58432f5044bef6b155/cc/ipc/BUILD.gn
[add] https://crrev.com/fd24c28f0f2c34d919703c58432f5044bef6b155/cc/ipc/display_compositor.mojom
[modify] https://crrev.com/fd24c28f0f2c34d919703c58432f5044bef6b155/services/ui/surfaces/BUILD.gn
[modify] https://crrev.com/fd24c28f0f2c34d919703c58432f5044bef6b155/services/ui/surfaces/display_compositor.cc
[modify] https://crrev.com/fd24c28f0f2c34d919703c58432f5044bef6b155/services/ui/surfaces/display_compositor.h
[delete] https://crrev.com/6a61226017202d545eeb01b92b96936f8efcb583/services/ui/surfaces/display_compositor_client.h
[modify] https://crrev.com/fd24c28f0f2c34d919703c58432f5044bef6b155/services/ui/ws/BUILD.gn
[modify] https://crrev.com/fd24c28f0f2c34d919703c58432f5044bef6b155/services/ui/ws/window_server.cc
[modify] https://crrev.com/fd24c28f0f2c34d919703c58432f5044bef6b155/services/ui/ws/window_server.h

2 is fixed: FrameGenerator no longer depends directly on ServerWindowCompositorFrameSink::window()

1.  window()->delegate()->OnScheduleWindowPaint(window()) should go away once FrameGenerator receives BeginFrames. (soonish)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb

commit d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb
Author: fsamuel <fsamuel@chromium.org>
Date: Wed Nov 02 15:50:52 2016

Mus+Ash: Unify CompositorFrameSinks

This CL moves towards enabling unified BeginFrame in Mus and splitting
the display compositor out of the window server.

1. FrameGenerator now submits CompositorFrames to the root window's
CompositorFrameSink instead of a special "DisplayCompositorFrameSink".
2. ServerWindowCompositorFrameSinks that have a valid AcceleratedWidget
will get a cc::Display (this should become SurfaceHandle when ready).

In an upcoming CL, FrmaeGenerator will no longer need to be aware of
GpuChannelHost. Instead it will simply use the root window's
CompositorFrameSink as is.

BUG= 658988 

Review-Url: https://codereview.chromium.org/2471503002
Cr-Commit-Position: refs/heads/master@{#429286}

[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/surfaces/BUILD.gn
[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/surfaces/direct_output_surface.h
[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/surfaces/direct_output_surface_ozone.h
[delete] https://crrev.com/c08c078b27b353f4ab8de7deccfb862270b1ff2a/services/ui/surfaces/display_compositor_frame_sink.cc
[delete] https://crrev.com/c08c078b27b353f4ab8de7deccfb862270b1ff2a/services/ui/surfaces/display_compositor_frame_sink.h
[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/surfaces/surfaces_context_provider.h
[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/ws/BUILD.gn
[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/ws/frame_generator.cc
[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/ws/frame_generator.h
[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/ws/server_window.cc
[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/ws/server_window.h
[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/ws/server_window_compositor_frame_sink.cc
[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/ws/server_window_compositor_frame_sink.h
[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/ws/server_window_compositor_frame_sink_manager.cc
[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/ws/server_window_compositor_frame_sink_manager.h
[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/ws/window_tree.cc
[modify] https://crrev.com/d2f1931ecdde26742abf7cc23f79b38d1dfaf7fb/services/ui/ws/window_tree.h