The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134

commit 49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134
Author: malaykeshav <malaykeshav@chromium.org>
Date: Wed May 10 11:20:53 2017

Implements a display scale tray setting behind a chrome switch

Implements a system tray setting to update and force a device scale factor
on the device. This tray setting is hidden behind a switch. This will help in debugging and testing UI at different scales faster.

Also adds a utility method to display class to force a new device scale
factor.

COMPONENT=System Tray, Ash switches, Ash strings, about flags, display
BUG= 718639 

Review-Url: https://codereview.chromium.org/2855143004
Cr-Commit-Position: refs/heads/master@{#470531}

[modify] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ash/BUILD.gn
[modify] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ash/ash_strings.grd
[modify] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ash/ash_switches.cc
[modify] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ash/ash_switches.h
[add] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ash/system/display_scale/scale_detailed_view.cc
[add] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ash/system/display_scale/scale_detailed_view.h
[add] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ash/system/display_scale/scale_view.cc
[add] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ash/system/display_scale/scale_view.h
[add] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ash/system/display_scale/tray_scale.cc
[add] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ash/system/display_scale/tray_scale.h
[modify] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ash/system/tray/system_tray.cc
[modify] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ash/system/tray/system_tray.h
[modify] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ui/display/display.cc
[modify] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ui/display/display.h
[modify] https://crrev.com/49cd16f6b9d7512e5cbcc02b41434d8e6cfe7134/ui/display/display_unittest.cc