yamaguchi@: Please take a look. Thank you.

I think we should punt this to M-70 because
- with the latest M69 branch the new uber tray will not be used
- this is a cosmetic issue
- this happens only on a non-default setting

This is a wider issue potentially affecting other parts of the System UI.

In views::Separator view,
https://cs.chromium.org/chromium/src/ui/views/controls/separator.cc?sq=package:chromium&g=0&rcl=dcef1b73d8797d2e7d337601f9fa16c362ee91aa&l=53
https://codereview.chromium.org/2675983003

When the device scale factor is smaller than 1, for example, when it's 1 - eps,
x=0, right=1-eps
gfx::ToEnclosedRect makes them into
x=ceil(0)=0, right=floor(1-eps)=0
Thus the width of the separators becomes zero.

I've found caroline device is not affected by this issue, seemingly because it has higher pixel density.
The default device scale of caroline is 2, and the minumum zoom by [ctrl]+[shift]+[-] is 0.5. The product doesn't go below 1 under this device.
So this needs to be verified on devices with device scale factor less than 2.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7a1501b5cdd841d45252c7cfd08380c7b703cfd8

commit 7a1501b5cdd841d45252c7cfd08380c7b703cfd8
Author: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Date: Tue Sep 25 08:24:04 2018

Keep 1px minimum thickness of Separator.

Prevents separator lines disappearing when the screen is zoomed out.
The issue would have happened on a device with scale factor 1.25, and
when it's zoomed out to the smallest. (1.25*0.7=0.825 < 1).
Other devices didn't have zoom preset that made the thickness below
1dp. See ui/display/manager/display_util.cc for detail.

Test: views_unittests --gtest_filter=SeparatorTest*
Test: manual test by tweaking values in display_util.cc
Bug:  864438 
Change-Id: I43842ee053ad77323503eadf114bbc5b9d2e2653
Reviewed-on: https://chromium-review.googlesource.com/1206530
Commit-Queue: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Evan Stade <estade@chromium.org>
Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593859}
[modify] https://crrev.com/7a1501b5cdd841d45252c7cfd08380c7b703cfd8/ui/views/BUILD.gn
[modify] https://crrev.com/7a1501b5cdd841d45252c7cfd08380c7b703cfd8/ui/views/controls/separator.cc
[add] https://crrev.com/7a1501b5cdd841d45252c7cfd08380c7b703cfd8/ui/views/controls/separator_unittest.cc

This bug requires manual review: M70 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: benmason@(Android), kariahda@(iOS), geohsu@(ChromeOS), abdulsyed@(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/+/fd4d500ac143e3f97bad9b96f68ab2aec8357b7a

commit fd4d500ac143e3f97bad9b96f68ab2aec8357b7a
Author: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Date: Thu Sep 27 01:31:33 2018

Keep 1px minimum thickness of Separator.

Prevents separator lines disappearing when the screen is zoomed out.
The issue would have happened on a device with scale factor 1.25, and
when it's zoomed out to the smallest. (1.25*0.7=0.825 < 1).
Other devices didn't have zoom preset that made the thickness below
1dp. See ui/display/manager/display_util.cc for detail.

Test: views_unittests --gtest_filter=SeparatorTest*
Test: manual test by tweaking values in display_util.cc
Bug:  864438 
Change-Id: I43842ee053ad77323503eadf114bbc5b9d2e2653
Reviewed-on: https://chromium-review.googlesource.com/1206530
Commit-Queue: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Evan Stade <estade@chromium.org>
Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#593859}(cherry picked from commit 7a1501b5cdd841d45252c7cfd08380c7b703cfd8)
Reviewed-on: https://chromium-review.googlesource.com/1247861
Reviewed-by: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Cr-Commit-Position: refs/branch-heads/3538@{#697}
Cr-Branched-From: 79f7c91a2b2a2932cd447fa6f865cb6662fa8fa6-refs/heads/master@{#587811}
[modify] https://crrev.com/fd4d500ac143e3f97bad9b96f68ab2aec8357b7a/ui/views/BUILD.gn
[modify] https://crrev.com/fd4d500ac143e3f97bad9b96f68ab2aec8357b7a/ui/views/controls/separator.cc
[add] https://crrev.com/fd4d500ac143e3f97bad9b96f68ab2aec8357b7a/ui/views/controls/separator_unittest.cc

The following revision refers to this bug: 
https://chromium.googlesource.com/chromium/src.git/+/fd4d500ac143e3f97bad9b96f68ab2aec8357b7a

Commit: fd4d500ac143e3f97bad9b96f68ab2aec8357b7a
Author: yamaguchi@chromium.org
Commiter: yamaguchi@chromium.org
Date: 2018-09-27 01:31:33 +0000 UTC

Keep 1px minimum thickness of Separator.

Prevents separator lines disappearing when the screen is zoomed out.
The issue would have happened on a device with scale factor 1.25, and
when it's zoomed out to the smallest. (1.25*0.7=0.825 < 1).
Other devices didn't have zoom preset that made the thickness below
1dp. See ui/display/manager/display_util.cc for detail.

Test: views_unittests --gtest_filter=SeparatorTest*
Test: manual test by tweaking values in display_util.cc
Bug:  864438 
Change-Id: I43842ee053ad77323503eadf114bbc5b9d2e2653
Reviewed-on: https://chromium-review.googlesource.com/1206530
Commit-Queue: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Evan Stade <estade@chromium.org>
Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#593859}(cherry picked from commit 7a1501b5cdd841d45252c7cfd08380c7b703cfd8)
Reviewed-on: https://chromium-review.googlesource.com/1247861
Reviewed-by: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Cr-Commit-Position: refs/branch-heads/3538@{#697}
Cr-Branched-From: 79f7c91a2b2a2932cd447fa6f865cb6662fa8fa6-refs/heads/master@{#587811}