Added Ash.SystemMenu.DefaultView.VisibleItems histogram.

ash/common/system/tray/system_tray_item.h

Index: ash/common/system/tray/system_tray_item.h
diff --git a/ash/common/system/tray/system_tray_item.h b/ash/common/system/tray/system_tray_item.h
index 09c5f82d7112e85599fcfc318b4d4bdf1fca17f6..87935abac1c867dd9131315a205b6ba83396c4fa 100644
--- a/ash/common/system/tray/system_tray_item.h
+++ b/ash/common/system/tray/system_tray_item.h
@@ -16,11 +16,46 @@ class View;
 
 namespace ash {
 class SystemTray;
+class SystemTrayBubble;
 class TrayItemView;
 
 class ASH_EXPORT SystemTrayItem {
  public:
-  explicit SystemTrayItem(SystemTray* system_tray);
+  // The different types of SystemTrayItems.
+  //
+  // *** IMPORTANT *** - These values are used for UMA metrics so do NOT

[James Cook, 2016/07/20 20:13:49]

nit: This probably doesn't need to be "**** IMPORTANT". We have this warning
lots of places in the code. "NOTE" or something less dire would be fine. :-)

[bruthig, 2016/07/21 14:34:58]

Done.

+  // re-order this enum and only insert items before the COUNT item.
+  enum UmaType {
+    TEST,                  // 0 - Used for test only.

[James Cook, 2016/07/20 20:13:49]

I would either give these all a prefix (like UMA_TYPE_AUDIO or UMA_AUDIO) or
make this an enum class. I find the call sites to the constructor a little odd
when they pass a bare "AUDIO" param.

[bruthig, 2016/07/21 14:34:58]

Done.

+    ACCESSIBILITY,         // 1

[James Cook, 2016/07/20 20:13:49]

nit: Don't explicitly number the enum in comments. I would just put = 0 on the
test item and leave its comment, or put "= <num>" after each item.  We have
precedent for both:

https://cs.chromium.org/chromium/src/extensions/common/constants.h?q=used.*um...

https://cs.chromium.org/chromium/src/chrome/browser/plugins/plugin_finder.cc?...

[bruthig, 2016/07/21 14:34:58]

Done.

+    AUDIO,                 // 2
+    BLUETOOTH,             // 3
+    CAPS_LOCK,             // 4
+    CAST,                  // 5
+    DATE,                  // 6
+    DISPLAY,               // 7
+    DISPLAY_BRIGHTNESS,    // 8
+    ENTERPRISE,            // 9
+    IME,                   // 10
+    MULTI_PROFILE_MEDIA,   // 11
+    NETWORK,               // 12
+    SETTINGS,              // 13
+    UPDATE,                // 14
+    POWER,                 // 15
+    ROTATION_LOCK,         // 16
+    SCREEN_CAPTURE,        // 17
+    SCREEN_SHARE,          // 18
+    SESSION_LENGTH_LIMIT,  // 19
+    SMS,                   // 20
+    SUPERVISED_USER,       // 21
+    TRACING,               // 22
+    USER,                  // 23
+    USER_SEPARATOR,        // 24
+    VPN,                   // 25
+    COUNT                  // 26
+  };
+
+  SystemTrayItem(SystemTray* system_tray, UmaType type);
   virtual ~SystemTrayItem();
 
   // Create* functions may return NULL if nothing should be displayed for the
@@ -107,7 +142,13 @@ class ASH_EXPORT SystemTrayItem {
   void set_restore_focus(bool restore_focus) { restore_focus_ = restore_focus; }
 
  private:
+  // Accesses uma_type().
+  friend class SystemTrayBubble;
+
+  UmaType uma_type() const { return uma_type_; }

[James Cook, 2016/07/20 20:13:49]

nit: If this is only used in test, eliminate and directly use |uma_type_|

[bruthig, 2016/07/21 14:34:58]

This is used by the SystemTrayBubble class in production.

+
   SystemTray* system_tray_;
+  UmaType uma_type_;
   bool restore_focus_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemTrayItem);