Added Ash.SystemMenu.DefaultView.VisibleItems histogram.

ash/common/system/tray/system_tray_bubble.h

Index: ash/common/system/tray/system_tray_bubble.h
diff --git a/ash/common/system/tray/system_tray_bubble.h b/ash/common/system/tray/system_tray_bubble.h
index 7714710d6c2be3ec42391d64c7855cbd2a059cc0..1fed352185ec5c244d4d4469cb5041712a895b13 100644
--- a/ash/common/system/tray/system_tray_bubble.h
+++ b/ash/common/system/tray/system_tray_bubble.h
@@ -5,10 +5,12 @@
 #ifndef ASH_COMMON_SYSTEM_TRAY_SYSTEM_TRAY_BUBBLE_H_
 #define ASH_COMMON_SYSTEM_TRAY_SYSTEM_TRAY_BUBBLE_H_
 
+#include <map>
 #include <memory>
 #include <vector>
 
 #include "ash/common/login_status.h"
+#include "ash/common/system/tray/system_tray_item.h"
 #include "base/macros.h"
 #include "base/timer/timer.h"
 #include "ui/views/bubble/tray_bubble_view.h"
@@ -59,6 +61,10 @@ class SystemTrayBubble {
   // ShouldShowShelf().
   bool ShouldShowShelf() const;
 
+  // Records metrics for visible system menu rows. Only implemented for the
+  // BUBBLE_TYPE_DEFAULT BubbleType.
+  void RecordVisibleRowMetrics();
+
  private:
   void CreateItemViews(LoginStatus login_status);
 
@@ -67,6 +73,9 @@ class SystemTrayBubble {
   std::vector<ash::SystemTrayItem*> items_;
   BubbleType bubble_type_;
 
+  // Tracks the views created in the last call to CreateItemViews().
+  std::map<SystemTrayItem::UmaType, views::View*> tray_item_view_map_;
+
   int autoclose_delay_;
   base::OneShotTimer autoclose_;