Track when and how a profile is signed out via UMA.

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 2a943cb11316f9c07a4184aa0e3f5a312f447a5c..d52b5e2591bd973ff91bcfd7b85b3d27ebe5966e 100644
--- a/components/signin/core/browser/signin_manager.cc
+++ b/components/signin/core/browser/signin_manager.cc
@@ -17,6 +17,7 @@
 #include "components/signin/core/browser/signin_client.h"
 #include "components/signin/core/browser/signin_internals_util.h"
 #include "components/signin/core/browser/signin_manager_cookie_helper.h"
+#include "components/signin/core/browser/signin_metrics.h"
 #include "components/signin/core/common/signin_pref_names.h"
 #include "google_apis/gaia/gaia_auth_util.h"
 #include "google_apis/gaia/gaia_urls.h"
@@ -235,6 +236,8 @@ void SigninManager::Initialize(PrefService* local_state) {
   if ((!user.empty() && !IsAllowedUsername(user)) || !IsSigninAllowed()) {
     // User is signed in, but the username is invalid - the administrator must
     // have changed the policy since the last signin, so sign out the user.
+    signin_metrics::LogSignout(
+        signin_metrics::SIGNIN_PREF_CHANGED_DURING_SIGNIN);
     SignOut();
   }
 
@@ -257,6 +260,8 @@ void SigninManager::OnGoogleServicesUsernamePatternChanged() {
       !IsAllowedUsername(GetAuthenticatedUsername())) {
     // Signed in user is invalid according to the current policy so sign
     // the user out.
+    signin_metrics::LogSignout(
+        signin_metrics::GOOGLE_SERVICE_NAME_PATTERN_CHANGED);
     SignOut();
   }
 }
@@ -266,8 +271,10 @@ bool SigninManager::IsSigninAllowed() const {
 }
 
 void SigninManager::OnSigninAllowedPrefChanged() {
-  if (!IsSigninAllowed())
+  if (!IsSigninAllowed()) {
+    signin_metrics::LogSignout(signin_metrics::SIGNOUT_PREF_CHANGED);
     SignOut();
+  }
 }
 
 // static