Add a SigninAllowed policy.

chrome/browser/managed_mode/managed_user_service.cc

 // Copyright (c) 2013 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 "chrome/browser/managed_mode/managed_user_service.h"
 
 #include "base/memory/ref_counted.h"
 #include "base/sequenced_task_runner.h"
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/extensions/extension_system.h"
@@ skipping 96 matching lines @@
 
 // static
 void ManagedUserService::RegisterUserPrefs(PrefServiceSyncable* prefs) {
   prefs->RegisterListPref(prefs::kManagedModeWhitelist,
                           PrefServiceSyncable::UNSYNCABLE_PREF);
   prefs->RegisterListPref(prefs::kManagedModeBlacklist,
                           PrefServiceSyncable::UNSYNCABLE_PREF);
   prefs->RegisterIntegerPref(prefs::kDefaultManagedModeFilteringBehavior,
                              ManagedModeURLFilter::BLOCK,
                              PrefServiceSyncable::UNSYNCABLE_PREF);
+  prefs->RegisterBooleanPref(prefs::kManagedUserNoSignin,

[Pam (message me for reviews), 2013/01/30 10:03:41]

There are a lot of old counterexamples, but we've decided more recently to
express prefs and policies as "allow" rather than "disable", to avoid
double-negatives ("disable is true").

+                             false,
+                             PrefServiceSyncable::UNSYNCABLE_PREF);
 }
 
 scoped_refptr<const ManagedModeURLFilter>
 ManagedUserService::GetURLFilterForIOThread() {
   return url_filter_context_.io_url_filter();
 }
 
 ManagedModeURLFilter* ManagedUserService::GetURLFilterForUIThread() {
   return url_filter_context_.ui_url_filter();
 }
@@ skipping 217 matching lines @@
 scoped_ptr<base::ListValue> ManagedUserService::GetWhitelist() {
   return make_scoped_ptr(
       profile_->GetPrefs()->GetList(prefs::kManagedModeWhitelist)->DeepCopy());
 }
 
 void ManagedUserService::AddURLPatternToManualList(
     bool is_whitelist,
     const std::string& url_pattern) {
   url_filter_context_.AddURLPatternToManualList(true, url_pattern);
 }