Implements a display scale tray setting behind a chrome switch

ash/system/tray/system_tray.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/system/tray/system_tray.h"
 
 #include <algorithm>
 #include <map>
 #include <vector>
 
 #include "ash/key_event_watcher.h"
 #include "ash/login_status.h"
 #include "ash/public/cpp/shell_window_ids.h"
 #include "ash/root_window_controller.h"
 #include "ash/session/session_controller.h"
 #include "ash/shelf/wm_shelf.h"
 #include "ash/shell.h"
 #include "ash/shell_port.h"
 #include "ash/strings/grit/ash_strings.h"
 #include "ash/system/audio/tray_audio.h"
 #include "ash/system/bluetooth/tray_bluetooth.h"
 #include "ash/system/brightness/tray_brightness.h"
 #include "ash/system/cast/tray_cast.h"
 #include "ash/system/date/tray_system_info.h"
+#include "ash/system/display_scale/tray_scale.h"
 #include "ash/system/enterprise/tray_enterprise.h"
 #include "ash/system/ime/tray_ime_chromeos.h"
 #include "ash/system/media_security/multi_profile_media_tray_item.h"
 #include "ash/system/network/tray_network.h"
 #include "ash/system/network/tray_vpn.h"
 #include "ash/system/night_light/tray_night_light.h"
 #include "ash/system/power/power_status.h"
 #include "ash/system/power/tray_power.h"
 #include "ash/system/screen_security/screen_capture_tray_item.h"
 #include "ash/system/screen_security/screen_share_tray_item.h"
@@ skipping 230 matching lines @@
   AddTrayItem(base::MakeUnique<TrayBluetooth>(this));
   tray_cast_ = new TrayCast(this);
   AddTrayItem(base::WrapUnique(tray_cast_));
   screen_capture_tray_item_ = new ScreenCaptureTrayItem(this);
   AddTrayItem(base::WrapUnique(screen_capture_tray_item_));
   screen_share_tray_item_ = new ScreenShareTrayItem(this);
   AddTrayItem(base::WrapUnique(screen_share_tray_item_));
   AddTrayItem(base::MakeUnique<MultiProfileMediaTrayItem>(this));
   tray_audio_ = new TrayAudio(this);
   AddTrayItem(base::WrapUnique(tray_audio_));
+  tray_scale_ = new TrayScale(this);
+  AddTrayItem(base::WrapUnique(tray_scale_));
   AddTrayItem(base::MakeUnique<TrayBrightness>(this));
   AddTrayItem(base::MakeUnique<TrayCapsLock>(this));
   tray_night_light_ = new TrayNightLight(this);
   AddTrayItem(base::WrapUnique(tray_night_light_));
   // TODO(jamescook): Remove this when mus has support for display management
   // and we have a DisplayManager equivalent. See http://crbug.com/548429
   std::unique_ptr<SystemTrayItem> tray_rotation_lock =
       delegate->CreateRotationLockTrayItem(this);
   if (tray_rotation_lock)
     AddTrayItem(std::move(tray_rotation_lock));
@@ skipping 432 matching lines @@
           .work_area()
           .height();
   if (work_area_height > 0) {
     UMA_HISTOGRAM_CUSTOM_COUNTS(
         "Ash.SystemMenu.PercentageOfWorkAreaHeightCoveredByMenu",
         100 * bubble_view->height() / work_area_height, 1, 300, 100);
   }
 }
 
 }  // namespace ash