UMA track signed in duration at signout

components/signin/core/common/signin_pref_names.cc

 // Copyright 2014 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.
 
 #include "components/signin/core/common/signin_pref_names.h"
 
 namespace prefs {
 
 // Boolean identifying whether reverse auto-login is enabled.
 const char kAutologinEnabled[] = "autologin.enabled";
@@ skipping 25 matching lines @@
     "google.services.username_pattern";
 
 // Boolean identifying whether reverse auto-logins is enabled.
 const char kReverseAutologinEnabled[] = "reverse_autologin.enabled";
 
 // List to keep track of emails for which the user has rejected one-click
 // sign-in.
 const char kReverseAutologinRejectedEmailList[] =
     "reverse_autologin.rejected_email_list";
 
+// Int64 which tracks, as time from epoch, when last time the user signed in
+// to the browser.
+const char kSignedInTime[] = "signin.signedin_time";
+
 // Boolean which stores if the user is allowed to signin to chrome.
 const char kSigninAllowed[] = "signin.allowed";
 
 }  // namespace prefs