cros: Add enterprise user session metrics

chrome/browser/chromeos/session_length_limiter.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_CHROMEOS_SESSION_LENGTH_LIMITER_H_
 #define CHROME_BROWSER_CHROMEOS_SESSION_LENGTH_LIMITER_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
@@ skipping 19 matching lines @@
     virtual const base::TimeTicks GetCurrentTime() const = 0;
     virtual void StopSession() = 0;
   };
 
   // Registers preferences.
   static void RegisterPrefs(PrefRegistrySimple* registry);
 
   SessionLengthLimiter(Delegate* delegate, bool browser_restarted);
   ~SessionLengthLimiter() override;
 
+  // Returns the duration between |session_start_time_| and now if there is a
+  // valid |session_start_time_|. Otherwise, returns 0.
+  base::TimeDelta GetSessionDuration() const;
+
   // ui::UserActivityObserver:
   void OnUserActivity(const ui::Event* event) override;
 
  private:
   // Attempt to restore the session start time and the flag indicating user
   // activity from local state. Return |true| if the restore is successful.
   bool RestoreStateAfterCrash();
 
   // Update the session start time if possible:
   // * If instructed to wait for initial user activity, the session start time
@@ skipping 16 matching lines @@
   std::unique_ptr<base::OneShotTimer> timer_;
   base::TimeTicks session_start_time_;
   bool user_activity_seen_;
 
   DISALLOW_COPY_AND_ASSIGN(SessionLengthLimiter);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_SESSION_LENGTH_LIMITER_H_