Is this on canary or beta channel?

yiyix@, could it be your recent change?

#1, I can see it in dev - 57.0.2970.0 on samus.

It is due to my changes. Sorry i didn't notice it when i test the UI. 

This bug is due to changes in this, https://bugs.chromium.org/p/chromium/issues/detail?id=657211,
and it had made to M56. I will fix it and request to merge to M56. 

FYI https://bugs.chromium.org/p/chromium/issues/detail?id=657211 hasn't been merged to M56 yet.  We can wait until this fix is ready and merge both together.

@sgabriel, could you please correct the bug description? This bug should always appear.

Note that I see this consistently on dev channel in Guest mode.

Issue 677200 has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ee16fc4f187bb47b7a2a0535c59ae9feb152a169

commit ee16fc4f187bb47b7a2a0535c59ae9feb152a169
Author: yiyix <yiyix@chromium.org>
Date: Tue Jan 10 05:49:29 2017

Remove the extra separator appears on the right side of the shelf

TEST=MANUAL

BUG= 679427 

Review-Url: https://codereview.chromium.org/2618383003
Cr-Commit-Position: refs/heads/master@{#442502}

[modify] https://crrev.com/ee16fc4f187bb47b7a2a0535c59ae9feb152a169/ash/common/system/chromeos/session/logout_button_tray.cc
[modify] https://crrev.com/ee16fc4f187bb47b7a2a0535c59ae9feb152a169/ash/common/system/tray/system_tray.cc
[modify] https://crrev.com/ee16fc4f187bb47b7a2a0535c59ae9feb152a169/ash/common/system/tray/tray_background_view.cc
[modify] https://crrev.com/ee16fc4f187bb47b7a2a0535c59ae9feb152a169/ash/common/system/tray/tray_background_view.h

Your change meets the bar and is auto-approved for M56. Please go ahead and merge the CL manually. Please contact milestone owner if you have questions.
Owners: amineer@(clank), cmasso@(bling), gkihumba@(cros), bustamante@(desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5aa9a1cdb8ccc25e665ace40f12f7d4a0bafe1e5

commit 5aa9a1cdb8ccc25e665ace40f12f7d4a0bafe1e5
Author: Ben Ruthig <bruthig@chromium.org>
Date: Wed Jan 11 15:21:11 2017

Remove the extra separator appears on the right side of the shelf

TEST=MANUAL

BUG= 679427 

Review-Url: https://codereview.chromium.org/2618383003
Cr-Commit-Position: refs/heads/master@{#442502}
(cherry picked from commit ee16fc4f187bb47b7a2a0535c59ae9feb152a169)

Review-Url: https://codereview.chromium.org/2621323003 .
Cr-Commit-Position: refs/branch-heads/2924@{#731}
Cr-Branched-From: 3a87aecc31cd1ffe751dd72c04e5a96a1fc8108a-refs/heads/master@{#433059}

[modify] https://crrev.com/5aa9a1cdb8ccc25e665ace40f12f7d4a0bafe1e5/ash/common/system/chromeos/session/logout_button_tray.cc
[modify] https://crrev.com/5aa9a1cdb8ccc25e665ace40f12f7d4a0bafe1e5/ash/common/system/tray/system_tray.cc
[modify] https://crrev.com/5aa9a1cdb8ccc25e665ace40f12f7d4a0bafe1e5/ash/common/system/tray/tray_background_view.cc
[modify] https://crrev.com/5aa9a1cdb8ccc25e665ace40f12f7d4a0bafe1e5/ash/common/system/tray/tray_background_view.h

Verified on ChromeOS 9202.0.0, 57.0.2984.0

Also verified on 9000.66.0, 56.0.2924.67