The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b7103ec2b3207beda523fe49472fb4b2c1259edb

commit b7103ec2b3207beda523fe49472fb4b2c1259edb
Author: Weidong Guo <weidongg@chromium.org>
Date: Thu Nov 16 06:34:57 2017

Fix display layout in UI settings for multi-mirroring

Changes:
Show correct number of displays in the layout in the display settings.

Specs: https://screenshot.googleplex.com/2nDXdwpsagu
Screenshot: https://screenshot.googleplex.com/YsvtJKF0Nei

BUG= 784623 

Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I179f256c1528da35511d1a7e0d1b0a6836297ec9
Reviewed-on: https://chromium-review.googlesource.com/767648
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Toni Barzic <tbarzic@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517001}
[modify] https://crrev.com/b7103ec2b3207beda523fe49472fb4b2c1259edb/chrome/browser/extensions/display_info_provider_chromeos.cc
[modify] https://crrev.com/b7103ec2b3207beda523fe49472fb4b2c1259edb/chrome/browser/resources/settings/device_page/display.js
[modify] https://crrev.com/b7103ec2b3207beda523fe49472fb4b2c1259edb/chrome/browser/resources/settings/device_page/display_layout.html
[modify] https://crrev.com/b7103ec2b3207beda523fe49472fb4b2c1259edb/chrome/browser/resources/settings/device_page/display_layout.js
[modify] https://crrev.com/b7103ec2b3207beda523fe49472fb4b2c1259edb/extensions/common/api/system_display.idl
[modify] https://crrev.com/b7103ec2b3207beda523fe49472fb4b2c1259edb/third_party/closure_compiler/externs/system_display.js