It seems like Shell::OnSessionStateChanged is never called with an active session.
(that's the code path to initialize the shelf for the active session)
I'm digging a bit deeper, but passing to xiyuan@ for recent SessionController changes.

Probably related to refactoring I did this week, suspect one of the two:
https://chromium-review.git.corp.google.com/c/478054/
https://chromium-review.git.corp.google.com/c/478455/

Will take a closer look...

emm... seems like SessionController did not gets the call from SessionControllerClient somehow... Thus ash side session state is not updated.

Reverting https://chromium-review.googlesource.com/c/478455/ didn't help.
Reverting https://chromium-review.git.corp.google.com/c/478054/ doesn't build cleanly.

Let me know if you want some help digging, but you probably have a better idea of SessionControllerClient behavior.

Are we sure this worked last week? I have gone back to r462971 (Apr 7) and did not see the shelf.

I am running chrome with "--user-data-dir=<> --mus". Is that the correct command line to use?

Scott should confirm. I never actually ran chrome --mus before. FYI, running with --login-manager --mus also shows no shelf, but pulls this right desktop wallpaper.

I can't definitely say if the shelf worked last week. I thought it did, but I'm not 100% positive.

I suspect somehow mojo services in ash is not exposed properly.

Could the following line indicate failures to connect to interfaces in ash?

[5916:5939:0421/132521.212714:1097067889608:ERROR:instance.cc(71)] Unable to locate service manifest for ash
[5916:5939:0421/132521.212960:1097067889850:ERROR:service_manager.cc(884)] Failed to resolve service name: ash
...
[5916:5939:0421/132521.596196:1097068273089:ERROR:instance.cc(71)] Unable to locate service manifest for ash

In mushrome mode we shouldn't be connected to ash. I'll see if I can locate who is doing that.

I've seen these messages in the mus_browser_tests. There are currently a number of sites trying to bind to ash (https://cs.chromium.org/search/?q=ash::mojom::kServiceName&type=cs)

Those messages appear when they attempt to bind to the service, however it is not in the manifest, nor running separately.

But we would need to connect to the embedded ash service because SessionStateDelegate is replaced with mojo::SessionController and session state is only sent to ash via mojo now. This is the case with classic ash too. Can we enable embedded ash for mushroom mode?

Yep, you are right. I think the manifests are wrong for mushrome. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2b28384faa81887e11fe43ffa1e55c329f4da422

commit 2b28384faa81887e11fe43ffa1e55c329f4da422
Author: sky <sky@chromium.org>
Date: Sat Apr 22 00:00:18 2017

Fixs catalogs for mash/mus

The mus catalog wasn't referring to ash, which meant attempts to
connect to ash failed.

BUG= 714137 
TEST=none
R=rockot@chromium.org

Review-Url: https://codereview.chromium.org/2832943003
Cr-Commit-Position: refs/heads/master@{#466500}

[modify] https://crrev.com/2b28384faa81887e11fe43ffa1e55c329f4da422/chrome/app/BUILD.gn
[modify] https://crrev.com/2b28384faa81887e11fe43ffa1e55c329f4da422/chrome/app/mash/BUILD.gn
[modify] https://crrev.com/2b28384faa81887e11fe43ffa1e55c329f4da422/chrome/test/BUILD.gn