Add a SigninAllowed policy.

chrome/common/pref_names.h

 // Copyright (c) 2012 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.
 
 // Constants for the names of various preferences, for easier changing.
 
 #ifndef CHROME_COMMON_PREF_NAMES_H_
 #define CHROME_COMMON_PREF_NAMES_H_
 
 #include <stddef.h>
@@ skipping 578 matching lines @@
 extern const char kDevToolsHSplitLocation[];
 extern const char kDevToolsOpenDocked[];
 #if defined(OS_ANDROID)
 extern const char kDevToolsRemoteEnabled[];
 #endif
 extern const char kDevToolsVSplitLocation[];
 #if defined(OS_ANDROID)
 // Used by Chrome Mobile.
 extern const char kSpdyProxyEnabled[];
 #endif
+extern const char kSigninAllowed[];
 extern const char kSyncLastSyncedTime[];
 extern const char kSyncHasSetupCompleted[];
 extern const char kSyncKeepEverythingSynced[];
 extern const char kSyncBookmarks[];
 extern const char kSyncPasswords[];
 extern const char kSyncPreferences[];
 extern const char kSyncAppNotifications[];
 extern const char kSyncAppSettings[];
 extern const char kSyncApps[];
 extern const char kSyncAutofill[];
@@ skipping 251 matching lines @@
 extern const char kRLZDisabled[];
 #endif
 
 #if defined(ENABLE_APP_LIST)
 extern const char kAppListProfile[];
 #endif
 
 }  // namespace prefs
 
 #endif  // CHROME_COMMON_PREF_NAMES_H_