Added UMA metrics for screen capture UI in the status area.

ash/common/system/chromeos/screen_security/screen_tray_item.h

Index: ash/common/system/chromeos/screen_security/screen_tray_item.h
diff --git a/ash/common/system/chromeos/screen_security/screen_tray_item.h b/ash/common/system/chromeos/screen_security/screen_tray_item.h
index b670afb256a20306c0004c60a3f9600be502554d..9e0f0e0763bf10c67762e47cadd31876eee6c690 100644
--- a/ash/common/system/chromeos/screen_security/screen_tray_item.h
+++ b/ash/common/system/chromeos/screen_security/screen_tray_item.h
@@ -117,6 +117,12 @@ class ASH_EXPORT ScreenTrayItem : public SystemTrayItem {
   // Returns the id of the notification for the tray item.
   virtual std::string GetNotificationId() = 0;
 
+  // Called after Stop() is invoked from the default view.
+  virtual void RecordStoppedFromDefaultViewMetric();

[James Cook, 2016/07/08 21:50:21]

nit: I think it would be clearer if these were pure-virtual, and you put a
comment in the empty implementation in the subclass just saying it's intentional
that you aren't recording a metric.

+
+  // Called after Stop() is invoked from the notification view.
+  virtual void RecordStoppedFromNotificationViewMetric();
+
   // Overridden from SystemTrayItem.
   views::View* CreateTrayView(LoginStatus status) override = 0;
   views::View* CreateDefaultView(LoginStatus status) override = 0;