Add a SigninAllowed policy.

chrome/browser/signin/signin_manager_fake.cc

Index: chrome/browser/signin/signin_manager_fake.cc
diff --git a/chrome/browser/signin/signin_manager_fake.cc b/chrome/browser/signin/signin_manager_fake.cc
index 6b377c15431a515d4e4df4be372cb9d5faeebb2c..7f6df1d2fa539c90fbe643e56cf46e84907e3dd7 100644
--- a/chrome/browser/signin/signin_manager_fake.cc
+++ b/chrome/browser/signin/signin_manager_fake.cc
@@ -4,10 +4,14 @@
 
 #include "chrome/browser/signin/signin_manager_fake.h"
 
+#include "base/callback_helpers.h"
+#include "chrome/browser/prefs/pref_service.h"
+#include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/signin/signin_global_error.h"
 #include "chrome/browser/ui/global_error/global_error_service.h"
 #include "chrome/browser/ui/global_error/global_error_service_factory.h"
 #include "chrome/common/chrome_notification_types.h"
+#include "chrome/common/pref_names.h"
 #include "content/public/browser/notification_service.h"
 
 FakeSigninManager::FakeSigninManager(Profile* profile)
@@ -16,6 +20,9 @@ FakeSigninManager::FakeSigninManager(Profile* profile)
   signin_global_error_.reset(new SigninGlobalError(this, profile));
   GlobalErrorServiceFactory::GetForProfile(profile_)->AddGlobalError(
       signin_global_error_.get());
+  signin_allowed_.Init(prefs::kSigninAllowed, profile_->GetPrefs(),
+                       base::Bind(&SigninManager::OnSigninAllowedPrefChanged,
+                                  base::Unretained(this)));
 }
 
 FakeSigninManager::~FakeSigninManager() {