mash: Introduce WmSystemTrayNotifier for //ash/common

chrome/browser/ui/ash/system_tray_delegate_chromeos.h

Index: chrome/browser/ui/ash/system_tray_delegate_chromeos.h
diff --git a/chrome/browser/ui/ash/system_tray_delegate_chromeos.h b/chrome/browser/ui/ash/system_tray_delegate_chromeos.h
index 766db0729986e6e72cec83d9f13bb49f9a9144a9..c2d40550709c23762cb5563447799246d32d9f46 100644
--- a/chrome/browser/ui/ash/system_tray_delegate_chromeos.h
+++ b/chrome/browser/ui/ash/system_tray_delegate_chromeos.h
@@ -44,6 +44,7 @@
 #include "ui/chromeos/ime/input_method_menu_manager.h"
 
 namespace ash {
+class WmSystemTrayNotifier;
 class VPNDelegate;
 }
 
@@ -165,11 +166,12 @@ class SystemTrayDelegateChromeOS
   void OnSystemClockChanged(system::SystemClock*) override;
 
  private:
-
   ash::SystemTray* GetPrimarySystemTray();
 
   ash::SystemTrayNotifier* GetSystemTrayNotifier();
 
+  ash::WmSystemTrayNotifier* GetWmSystemTrayNotifier();
+
   void SetProfile(Profile* profile);
 
   bool UnsetProfile(Profile* profile);