Consolidate volume control code.

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 e2c5d7ce43d777ef8838bff7d9b2e780316e7b8e..1eb2052e42f1b8857bb5eaa32a888eb84ab445a3 100644
--- a/ash/system/tray/system_tray.h
+++ b/ash/system/tray/system_tray.h
@@ -93,6 +93,9 @@ class ASH_EXPORT SystemTray : public internal::TrayBackgroundView {
   // Updates the items when the login status of the system changes.
   void UpdateAfterLoginStatusChange(user::LoginStatus login_status);
 
+  // Updates the items after the OpenAsh() has initialized the shell.
+  void UpdateAfterAshInit();
+
   // Updates the items when the shelf alignment changes.
   void UpdateAfterShelfAlignmentChange(ShelfAlignment alignment);