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

chrome/browser/signin/signin_manager_factory.cc

Index: chrome/browser/signin/signin_manager_factory.cc
diff --git a/chrome/browser/signin/signin_manager_factory.cc b/chrome/browser/signin/signin_manager_factory.cc
index 10f458d7a3c6c1735c1bb8df5bf2a1324015e233..63fdc1b1468b7370aabc29315bdd5d44d7fb5fa7 100644
--- a/chrome/browser/signin/signin_manager_factory.cc
+++ b/chrome/browser/signin/signin_manager_factory.cc
@@ -15,7 +15,12 @@
 #include "chrome/browser/signin/profile_oauth2_token_service_factory.h"
 #include "components/keyed_service/content/browser_context_dependency_manager.h"
 #include "components/prefs/pref_registry_simple.h"
+
+#if !defined(OS_ANDROID) && !defined(OS_CHROMEOS)
+#include "chrome/browser/signin/force_signin_manager.h"
+#else
 #include "components/signin/core/browser/signin_manager.h"
+#endif
 
 SigninManagerFactory::SigninManagerFactory()
     : BrowserContextKeyedServiceFactory(
@@ -115,11 +120,19 @@ KeyedService* SigninManagerFactory::BuildServiceInstanceFor(
       client,
       AccountTrackerServiceFactory::GetForProfile(profile));
 #else
-  service = new SigninManager(
-      client,
-      ProfileOAuth2TokenServiceFactory::GetForProfile(profile),
-      AccountTrackerServiceFactory::GetForProfile(profile),
-      GaiaCookieManagerServiceFactory::GetForProfile(profile));
+#if !defined(OS_ANDROID)
+  if (ForceSigninManager::IsForceSigninEnabled())
+    service = new ForceSigninManager(
+        profile, client,
+        ProfileOAuth2TokenServiceFactory::GetForProfile(profile),
+        AccountTrackerServiceFactory::GetForProfile(profile),
+        GaiaCookieManagerServiceFactory::GetForProfile(profile));
+  else
+#endif
+    service = new SigninManager(
+        client, ProfileOAuth2TokenServiceFactory::GetForProfile(profile),
+        AccountTrackerServiceFactory::GetForProfile(profile),
+        GaiaCookieManagerServiceFactory::GetForProfile(profile));

[Roger Tawa OOO till Jul 10th, 2016/10/26 18:25:31]

Nit: add { and } around if and else blocks.

   AccountFetcherServiceFactory::GetForProfile(profile);
 #endif
   service->Initialize(g_browser_process->local_state());