Added Ash.SystemMenu.DefaultView.VisibleRows histogram.

ash/common/system/chromeos/network/tray_vpn.cc

Index: ash/common/system/chromeos/network/tray_vpn.cc
diff --git a/ash/common/system/chromeos/network/tray_vpn.cc b/ash/common/system/chromeos/network/tray_vpn.cc
index ac40d940c4a9737a4346cdb64bd0fbbd05f65cc1..10c28d0be36241502c66347a6f7b6bad2a56c4a7 100644
--- a/ash/common/system/chromeos/network/tray_vpn.cc
+++ b/ash/common/system/chromeos/network/tray_vpn.cc
@@ -112,7 +112,9 @@ class VpnDefaultView : public TrayItemMore,
 }  // namespace tray
 
 TrayVPN::TrayVPN(SystemTray* system_tray)
-    : SystemTrayItem(system_tray), default_(NULL), detailed_(NULL) {
+    : SystemTrayItem(system_tray, UMA_VPN),
+      default_(nullptr),
+      detailed_(nullptr) {
   network_state_observer_.reset(new TrayNetworkStateObserver(this));
 }