Override SigninManager::SignOut if force-signin is enabled.

components/signin/core/browser/signin_client.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_client.h"
 
 #include "base/guid.h"
 #include "base/logging.h"
 #include "components/prefs/pref_service.h"
 #include "components/signin/core/common/signin_pref_names.h"
@@ skipping 14 matching lines @@
   if (signin_scoped_device_id.empty()) {
     // If device_id doesn't exist then generate new and save in prefs.
     signin_scoped_device_id = GenerateSigninScopedDeviceID(false);
     DCHECK(!signin_scoped_device_id.empty());
     prefs->SetString(prefs::kGoogleServicesSigninScopedDeviceId,
                      signin_scoped_device_id);
   }
   return signin_scoped_device_id;
 }
 
+void SigninClient::PreSignOut(const base::Callback<void()>& sign_out) {
+  sign_out.Run();
+}
+
 void SigninClient::SignOut() {
   GetPrefs()->ClearPref(prefs::kGoogleServicesSigninScopedDeviceId);
   OnSignedOut();
 }