[Night Light] CL2: Ash and system tray work

ash/system/tray/system_tray.h

Index: ash/system/tray/system_tray.h
diff --git a/ash/system/tray/system_tray.h b/ash/system/tray/system_tray.h
index 5e5244d1441954ae5ebddf7339ddf1c5bf2d94d2..bffa9e7117b521799fd652fd1f10e51ae2728606 100644
--- a/ash/system/tray/system_tray.h
+++ b/ash/system/tray/system_tray.h
@@ -29,6 +29,7 @@ class TrayAudio;
 class TrayCast;
 class TrayEnterprise;
 class TrayNetwork;
+class TrayNightLight;
 class TraySupervisedUser;
 class TraySystemInfo;
 class TrayTiles;
@@ -49,6 +50,8 @@ class ASH_EXPORT SystemTray : public TrayBackgroundView,
 
   TrayUpdate* tray_update() { return tray_update_; }
 
+  TrayNightLight* tray_night_light() { return tray_night_light_; }
+
   // Calls TrayBackgroundView::Initialize(), creates the tray items, and
   // adds them to SystemTrayNotifier.
   void InitializeTrayItems(SystemTrayDelegate* delegate,
@@ -234,6 +237,7 @@ class ASH_EXPORT SystemTray : public TrayBackgroundView,
   TraySupervisedUser* tray_supervised_user_ = nullptr;
   TraySystemInfo* tray_system_info_ = nullptr;
   TrayUpdate* tray_update_ = nullptr;
+  TrayNightLight* tray_night_light_ = nullptr;
 
   // A reference to the Screen share and capture item.
   ScreenTrayItem* screen_capture_tray_item_ = nullptr;  // not owned