The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bc758d44cc3a893ac37fd54c991798aba7175698

commit bc758d44cc3a893ac37fd54c991798aba7175698
Author: vabr <vabr@chromium.org>
Date: Thu Apr 14 08:01:45 2016

Revert of Only create DockedBackgroundWidget as needed. (patchset #6 id:100001 of https://codereview.chromium.org/1882713004/ )

Reason for revert:
Broke ash_unittests. More info in  http://crbug.com/603419 .

BUG= 603419 

Original issue's description:
> Only create DockedBackgroundWidget as needed.
>
> This util widget shows up as a user window shelf icon in mash.
> Don't create this widget until it's needed (not used in mash).
>
> We currently put kShellWindowId_DockedContainer windows in mash::wm::mojom::Container::USER_WINDOWS, which might be okay in the long run, but even if we put them in a separate container, we would need UserWindowControllerImpl to track that container's set of user windows (to show shelf icons); so we would need to single out this widget as a non-user-window somehow.
>
> We currently don't support docking in mash, but if we choose to use ash's DockedWindowLayoutManager (and DockedBackgroundWidget), we'll need to avoid tracking this background widget as a user window.
>
> BUG=NONE
> TEST="mojo_runner mojo:mash_session" doesn't show a mysterious shelf icon at startup.
> R=sky@chromium.org
>
> Committed: https://crrev.com/14816ec6589c41b5a34f7b534b1c1565c97fe2d7
> Cr-Commit-Position: refs/heads/master@{#387182}

TBR=sky@chromium.org,msw@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=NONE

Review URL: https://codereview.chromium.org/1888733002

Cr-Commit-Position: refs/heads/master@{#387259}

[modify] https://crrev.com/bc758d44cc3a893ac37fd54c991798aba7175698/ash/wm/dock/docked_window_layout_manager.cc
[modify] https://crrev.com/bc758d44cc3a893ac37fd54c991798aba7175698/ash/wm/dock/docked_window_layout_manager.h

Which bot(s) broke? Please link to the failed builds.

It took some searching on flakiness dashboard:
http://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=ash_unittests&builder=chromium.chromiumos%3ALinux%20ChromiumOS%20Tests%20(dbg)(1)

But I found the actual failures on Linux ChromiumOS Tests (dbg)(1):
https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20(dbg)(1)/builds/13464
The only other bot I found that had these failures is MD Top Chrome ChromeOS material-hybrid:
https://build.chromium.org/p/chromium.fyi/builders/MD%20Top%20Chrome%20ChromeOS%20material-hybrid/builds/216

All three tests passed with my change on Linux ChromiumOS Tests (1) and the two trybots runs: https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20(1)/builds/18864
https://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_chromeos_ozone_rel_ng/builds/154339
https://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_chromeos_rel_ng/builds/196538

Luckily, I can also repro locally, so I should have a revised patch soon.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/21a784910f87c59e1db7d8034088d34268753d9d

commit 21a784910f87c59e1db7d8034088d34268753d9d
Author: msw <msw@chromium.org>
Date: Fri Apr 15 00:09:34 2016

Only create DockedBackgroundWidget as needed.

This util widget shows up as a user window shelf icon in mash.
Don't create this widget until it's needed (not used in mash).

We currently put kShellWindowId_DockedContainer windows in mash::wm::mojom::Container::USER_WINDOWS, which might be okay in the long run, but even if we put them in a separate container, we would need UserWindowControllerImpl to track that container's set of user windows (to show shelf icons); so we would need to single out this widget as a non-user-window somehow.

We currently don't support docking in mash, but if we choose to use ash's DockedWindowLayoutManager (and DockedBackgroundWidget), we'll need to avoid tracking this background widget as a user window.

BUG= 603419 
TEST="mojo_runner mojo:mash_session" doesn't show a mysterious shelf icon at startup.
R=sky@chromium.org

Committed: https://crrev.com/14816ec6589c41b5a34f7b534b1c1565c97fe2d7
Cr-Commit-Position: refs/heads/master@{#387182}

Review URL: https://codereview.chromium.org/1882713004

Cr-Commit-Position: refs/heads/master@{#387486}

[modify] https://crrev.com/21a784910f87c59e1db7d8034088d34268753d9d/ash/wm/dock/docked_window_layout_manager.cc
[modify] https://crrev.com/21a784910f87c59e1db7d8034088d34268753d9d/ash/wm/dock/docked_window_layout_manager.h

Should be fixed, please reopen or ping me if the relanded cl causes any test failures.

(Sorry for the missed links, not sure where I dropped them. Also, thanks for fixing!)