The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b60b28add25318406ab2ced6c4290f677662a5a9

commit b60b28add25318406ab2ced6c4290f677662a5a9
Author: yoshiki iguchi <yoshiki@chromium.org>
Date: Tue Aug 07 17:24:42 2018

Remove sidebar

The sidebar was the project which replaced the current system tray but
it was taken over by the unified system tray. So the sidebar was no
longer used. This CL removes the sidebar-related unused code.

Bug:  871665 
Change-Id: Iaea91177182bf87d8b09c00a9a38edfa78daedda
Reviewed-on: https://chromium-review.googlesource.com/1164815
Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Yoshiki Iguchi <yoshiki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581268}
[modify] https://crrev.com/b60b28add25318406ab2ced6c4290f677662a5a9/ash/BUILD.gn
[modify] https://crrev.com/b60b28add25318406ab2ced6c4290f677662a5a9/ash/public/cpp/ash_switches.cc
[modify] https://crrev.com/b60b28add25318406ab2ced6c4290f677662a5a9/ash/public/cpp/ash_switches.h
[modify] https://crrev.com/b60b28add25318406ab2ced6c4290f677662a5a9/ash/root_window_controller.cc
[modify] https://crrev.com/b60b28add25318406ab2ced6c4290f677662a5a9/ash/root_window_controller.h
[modify] https://crrev.com/b60b28add25318406ab2ced6c4290f677662a5a9/ash/shelf/shelf_layout_manager.cc
[delete] https://crrev.com/6ba139bfc881e3b1813637a5c72f41bc5d75db2b/ash/sidebar/sidebar.cc
[delete] https://crrev.com/6ba139bfc881e3b1813637a5c72f41bc5d75db2b/ash/sidebar/sidebar.h
[delete] https://crrev.com/6ba139bfc881e3b1813637a5c72f41bc5d75db2b/ash/sidebar/sidebar_params.h
[delete] https://crrev.com/6ba139bfc881e3b1813637a5c72f41bc5d75db2b/ash/sidebar/sidebar_widget.cc
[delete] https://crrev.com/6ba139bfc881e3b1813637a5c72f41bc5d75db2b/ash/sidebar/sidebar_widget.h
[modify] https://crrev.com/b60b28add25318406ab2ced6c4290f677662a5a9/ash/system/message_center/notification_tray.cc
[modify] https://crrev.com/b60b28add25318406ab2ced6c4290f677662a5a9/chrome/browser/about_flags.cc
[modify] https://crrev.com/b60b28add25318406ab2ced6c4290f677662a5a9/chrome/browser/flag_descriptions.cc
[modify] https://crrev.com/b60b28add25318406ab2ced6c4290f677662a5a9/chrome/browser/flag_descriptions.h