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..e38358f4e96a445dd04571a8674cf737070defdb 100644
--- a/ash/common/system/tray/system_tray_item.h
+++ b/ash/common/system/tray/system_tray_item.h
@@ -20,9 +20,45 @@ 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
+  // re-order
+  // this enum and only insert items before the COUNT item.

[tdanderson, 2016/07/19 21:58:40]

nit: awkward line break.

[bruthig, 2016/07/20 18:15:52]

Done.

+  enum ItemType {
+    ACCESSIBILITY,         // 0

[tdanderson, 2016/07/19 21:58:40]

Consider making UNKNOWN/NONE the 0-element, and use that in unittests rather
than NETWORK.

[bruthig, 2016/07/20 18:15:52]

Added TEST at 0.

+    AUDIO,                 // 1
+    BLUETOOTH,             // 2
+    CAPS_LOCK,             // 3
+    CAST,                  // 4
+    DATE_POWER_LOCK,       // 5
+    DISPLAY,               // 6
+    DISPLAY_BRIGHTNESS,    // 7
+    ENTERPRISE,            // 8
+    IME,                   // 9
+    MULTI_PROFILE_MEDIA,   // 10
+    NETWORK,               // 11
+    OS_SETTINGS,           // 12
+    OS_UPDATE,             // 13
+    POWER,                 // 14
+    ROTATION_LOCK,         // 15
+    SCREEN_CAPTURE,        // 16
+    SCREEN_SHARE,          // 17
+    SESSION_LENGTH_LIMIT,  // 18
+    SMS,                   // 19
+    SUPERVISED_USER,       // 20
+    TRACING,               // 21
+    USER,                  // 22
+    USER_SEPARATOR,        // 23
+    VPN,                   // 24
+    COUNT                  // 25
+  };
+
+  SystemTrayItem(SystemTray* system_tray, ItemType type);
   virtual ~SystemTrayItem();
 
+  ItemType type() const { return item_type_; }

[tdanderson, 2016/07/19 21:58:40]

I'm a bit concerned that having a public type() in SystemTrayItem may lead to
future misuse (e.g., someone calling type() and performing a static_cast when
inappropriate). At the very least maybe we want to call this something like
type_for_uma(), and perhaps make it private (and friend the caller). WDYT?

[bruthig, 2016/07/20 18:15:52]

Renamed ItemType as UmaType, moved uma_type() to private visibility and friended
SystemTrayBubble.

+
   // Create* functions may return NULL if nothing should be displayed for the
   // type of view. The default implementations return NULL.
 
@@ -108,6 +144,7 @@ class ASH_EXPORT SystemTrayItem {
 
  private:
   SystemTray* system_tray_;
+  ItemType item_type_;
   bool restore_focus_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemTrayItem);