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

components/signin/core/browser/signin_metrics.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/browser/signin_metrics.h"
 
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/user_metrics.h"
 
@@ skipping 41 matching lines @@
 }
 
 void LogSigninAddAccount() {
   // Account signin may fail for a wide variety of reasons. There is no
   // explicit false, but one can compare this value with the various UI
   // flows that lead to account sign-in, and deduce that the difference
   // counts the failures.
   UMA_HISTOGRAM_BOOLEAN("Signin.AddAccount", true);
 }
 
+void LogSignout(ProfileSignout metric) {
+  UMA_HISTOGRAM_ENUMERATION("Signin.SignoutProfile", metric,
+                            NUM_PROFILE_SIGNOUT_METRICS);
+}
+
 }  // namespace signin_metrics