Refactor AddScrollListItem() in system menu detailed views

ash/system/tray/hover_highlight_view.h

Index: ash/system/tray/hover_highlight_view.h
diff --git a/ash/system/tray/hover_highlight_view.h b/ash/system/tray/hover_highlight_view.h
index bdaf647d7c4675b15af375281edf07186c900384..4283c53564bc08ca77774cdbf58cc8bc48c0eaa2 100644
--- a/ash/system/tray/hover_highlight_view.h
+++ b/ash/system/tray/hover_highlight_view.h
@@ -69,6 +69,10 @@ class HoverHighlightView : public ActionableView {
   // Hide or show the right view.
   void SetRightViewVisible(bool visible);
 
+  // Sets text for the sub label. Precondition for this function is that
+  // |text_label_| is non-null.
+  void SetSubText(const base::string16& sub_text);
+
   // Allows view to expand its height. Size of unexapandable view is fixed and
   // equals to kTrayPopupItemHeight.
   void SetExpandable(bool expandable);