I'm currently reworking the existing code for  issue 590311 , by the way.

Yep. This issue is about detecting in mus whether a client is playing video. Since mus has more information available to it about the content of the windows, the hope is that it can use a more reliable mechanism for detecting a video. For example, instead of [or, in addition to] using a heuristic to determine whether a video is playing (which can fail with continuous scrolling, for example), we can inspect the contents of compositor frames the client submits. (e.g. https://codereview.chromium.org/2140783002)

Once mus detects video, it will need to notify the clients (ash, for example). We will likely use the same criteria as  issue 590311  for this notification (i.e. when to notify the client, how often etc.). Does that make sense?

Sure, makes sense. One thing to keep in mind is that the detection code was originally added in the pre-<video> days to detect Flash video. Will mus need to fall back to something closer to the current heuristics to continue to detect that? If we only needed to detect HTML5 video, I think that that's already not too difficult -- PowerSaveBlocker objects are currently created to keep the screen on, for example.

We may need to fall back to using similar heuristics for flash videos, yeah. But I am going to look to see if that can also be annotated into the submitted compositor frame for plugins.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/32d1097c5645c0e1b0f49f93502d4f4701b67cec

commit 32d1097c5645c0e1b0f49f93502d4f4701b67cec
Author: sadrul <sadrul@chromium.org>
Date: Sat Jul 30 05:26:21 2016

services/ui: Detect when a video is playing.

Compositor frames submitted by mus clients include a flag to indicate whether the
client is playing a video or not. This information is plumbed through from
cc::Layer to cc::LayerImpl to cc::CompositorFrame[Metadata].

BUG= 627140 
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel

Review-Url: https://codereview.chromium.org/2140783002
Cr-Commit-Position: refs/heads/master@{#408864}

[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/ipc/cc_param_traits_macros.h
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/ipc/compositor_frame_metadata.mojom
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/ipc/compositor_frame_metadata_struct_traits.cc
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/ipc/compositor_frame_metadata_struct_traits.h
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/ipc/struct_traits_unittest.cc
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/layers/layer.cc
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/layers/layer.h
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/layers/layer_impl.cc
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/layers/layer_impl.h
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/layers/layer_unittest.cc
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/layers/video_layer.cc
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/layers/video_layer_impl.cc
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/output/compositor_frame_metadata.h
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/proto/layer.proto
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/surfaces/surface_aggregator.cc
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/surfaces/surface_aggregator.h
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/trees/layer_tree_host_impl.cc
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/trees/layer_tree_host_impl.h
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/cc/trees/layer_tree_host_impl_unittest.cc
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/content/renderer/pepper/pepper_plugin_instance_impl.cc
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/services/ui/ws/frame_generator.cc
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/services/ui/ws/frame_generator.h
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/services/ui/ws/frame_generator_unittest.cc
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/services/ui/ws/server_window_surface.cc
[modify] https://crrev.com/32d1097c5645c0e1b0f49f93502d4f4701b67cec/services/ui/ws/server_window_surface.h

Note that this code has been removed and needs to be revisited.

I think the mus code (i.e. code in services/ui/ws) has been removed. The code in cc should still be functional, and it should be possible to use that from the display-compositor to detect when video is playing. It will then need to notify the WS about it too.

Bug scrub: Is this still needed for mash? If so, SingleProcessMash vs. Multiprocess mash?

This is done.