UMA track signed in duration at signout

components/signin/core/browser/signin_manager.cc

Index: components/signin/core/browser/signin_manager.cc
diff --git a/components/signin/core/browser/signin_manager.cc b/components/signin/core/browser/signin_manager.cc
index 9c68eb98915ca9b5c5c0d78a990e7c1bd2ac50b0..851bcb40c40a951190cbbb2b3b15908c71ce4c60 100644
--- a/components/signin/core/browser/signin_manager.cc
+++ b/components/signin/core/browser/signin_manager.cc
@@ -7,6 +7,7 @@
 #include <string>
 #include <vector>
 
+#include "base/metrics/histogram.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
@@ -201,13 +202,24 @@ void SigninManager::SignOut(
   ClearTransientSigninData();
 
   const std::string username = GetAuthenticatedUsername();
+  const base::Time signin_time =
+      base::Time::FromInternalValue(
+          client_->GetPrefs()->GetInt64(prefs::kSignedInTime));
   clear_authenticated_username();
   client_->GetPrefs()->ClearPref(prefs::kGoogleServicesUsername);
+  client_->GetPrefs()->ClearPref(prefs::kSignedInTime);
   client_->ClearSigninScopedDeviceId();
 
   // Erase (now) stale information from AboutSigninInternals.
   NotifyDiagnosticsObservers(USERNAME, "");
 
+  // Determine the duration the user was logged in and log that to UMA.
+  if (!signin_time.is_null()) {
+    base::TimeDelta signed_in_duration = base::Time::Now() - signin_time;

[Alexei Svitkine (slow), 2014/08/12 14:41:49]

Note: Be aware that if the user's machine time changes, you'll get inconsistent
results. But presumably that should be a minority of users.

[Mike Lerman, 2014/08/12 18:07:10]

I assume this will indeed be a very small proportion of users.

+    UMA_HISTOGRAM_COUNTS("Signin.SignedInDurationBeforeSignout",
+                         signed_in_duration.InMinutes()));

[Roger Tawa OOO till Jul 10th, 2014/08/12 14:14:52]

Should we be paranoid and check that delta > 0?

[Alexei Svitkine (slow), 2014/08/12 14:41:49]

I believe it should automatically go in the underflow bucket, so its "OK" in the
sense that there won't be any crashes etc.

[Mike Lerman, 2014/08/12 18:07:10]

Acknowledged.

+  }
+
   // Revoke all tokens before sending signed_out notification, because there
   // may be components that don't listen for token service events when the
   // profile is not connected to an account.