Added Ash.SystemMenu.DefaultView.VisibleRows histogram.

ash/system/chromeos/tray_display.cc

Index: ash/system/chromeos/tray_display.cc
diff --git a/ash/system/chromeos/tray_display.cc b/ash/system/chromeos/tray_display.cc
index 657987c24fab081b51a8dc1f807858a052b24003..e38fdc8563024a2f06a0032eededb68ec6dc0e08 100644
--- a/ash/system/chromeos/tray_display.cc
+++ b/ash/system/chromeos/tray_display.cc
@@ -319,7 +319,7 @@ class DisplayView : public ActionableView {
 };
 
 TrayDisplay::TrayDisplay(SystemTray* system_tray)
-    : SystemTrayItem(system_tray), default_(NULL) {
+    : SystemTrayItem(system_tray, UMA_DISPLAY), default_(nullptr) {
   Shell::GetInstance()->window_tree_host_manager()->AddObserver(this);
   UpdateDisplayInfo(NULL);
 }