Consolidate volume control code.

ash/system/tray/system_tray.cc

Index: ash/system/tray/system_tray.cc
diff --git a/ash/system/tray/system_tray.cc b/ash/system/tray/system_tray.cc
index f26ba46f4cec30ec904b46672f4bdf5788b2a099..6e9cd2dff743ba696288c5430ec929c9c17c4403 100644
--- a/ash/system/tray/system_tray.cc
+++ b/ash/system/tray/system_tray.cc
@@ -261,6 +261,14 @@ void SystemTray::UpdateAfterShelfAlignmentChange(ShelfAlignment alignment) {
   }
 }
 
+void SystemTray::UpdateAfterAshInit() {
+  for (std::vector<SystemTrayItem*>::iterator it = items_.begin();
+      it != items_.end();
+      ++it) {
+    (*it)->UpdateAfterAshInit();
+  }
+}
+
 void SystemTray::SetHideNotifications(bool hide_notifications) {
   if (notification_bubble_.get())
     notification_bubble_->SetVisible(!hide_notifications);