Add a SigninAllowed policy.

chrome/browser/ui/webui/options/browser_options_handler.cc

Index: chrome/browser/ui/webui/options/browser_options_handler.cc
diff --git a/chrome/browser/ui/webui/options/browser_options_handler.cc b/chrome/browser/ui/webui/options/browser_options_handler.cc
index 5b5816769e59c8d30deac58e4c3cede461955808..4a55e1e239046b7959aeba05f8766ce410b2be35 100644
--- a/chrome/browser/ui/webui/options/browser_options_handler.cc
+++ b/chrome/browser/ui/webui/options/browser_options_handler.cc
@@ -143,6 +143,7 @@ BrowserOptionsHandler::~BrowserOptionsHandler() {
   if (sync_service)
     sync_service->RemoveObserver(this);
 
+  profile_pref_registrar_.RemoveAll();
   if (default_browser_worker_.get())
     default_browser_worker_->ObserverDestroyed();
   if (template_url_service_)
@@ -580,6 +581,13 @@ void BrowserOptionsHandler::OnStateChanged() {
   SendProfilesInfo();
 }
 
+void BrowserOptionsHandler::OnSigninAllowedPrefChange() {
+  web_ui()->CallJavascriptFunction("BrowserOptions.updateSyncState",
+                                   *GetSyncStateDictionary());
+
+  SendProfilesInfo();
+}
+
 void BrowserOptionsHandler::PageLoadStarted() {
   page_initialized_ = false;
 }
@@ -647,9 +655,12 @@ void BrowserOptionsHandler::InitializeHandler() {
       prefs::kDefaultZoomLevel, prefs,
       base::Bind(&BrowserOptionsHandler::SetupPageZoomSelector,
                  base::Unretained(this)));
+  profile_pref_registrar_.Init(prefs);
+  profile_pref_registrar_.Add(prefs::kSigninAllowed,
+                   base::Bind(&BrowserOptionsHandler::OnSigninAllowedPrefChange,
+                              base::Unretained(this)));
 #if !defined(OS_CHROMEOS)
-  proxy_prefs_.Init(prefs);
-  proxy_prefs_.Add(prefs::kProxy,
+  profile_pref_registrar_.Add(prefs::kProxy,
                    base::Bind(&BrowserOptionsHandler::SetupProxySettingsSection,
                               base::Unretained(this)));
 #endif  // !defined(OS_CHROMEOS)
@@ -1061,6 +1072,10 @@ scoped_ptr<DictionaryValue> BrowserOptionsHandler::GetSyncStateDictionary() {
   scoped_ptr<DictionaryValue> sync_status(new DictionaryValue);
   ProfileSyncService* service(ProfileSyncServiceFactory::
       GetInstance()->GetForProfile(Profile::FromWebUI(web_ui())));
+  SigninManager* signin = SigninManagerFactory::GetForProfile(
+      Profile::FromWebUI(web_ui()));
+  DCHECK(signin);

[Andrew T Wilson (Slow), 2013/02/07 10:08:11]

I believe signin can be NULL for chromeos guest profiles. If you sync with ToT
you'll see a fix I landed for this case.

[Adrian Kuegel, 2013/02/07 11:09:21]

I merged it to ToT. Hopefully correctly :-)

+  sync_status->SetBoolean("signinAllowed", signin->IsSigninAllowed());
   sync_status->SetBoolean("syncSystemEnabled", !!service);
   if (!service)
     return sync_status.Pass();
@@ -1071,8 +1086,6 @@ scoped_ptr<DictionaryValue> BrowserOptionsHandler::GetSyncStateDictionary() {
 
   string16 status_label;
   string16 link_label;
-  SigninManager* signin = SigninManagerFactory::GetForProfile(
-      Profile::FromWebUI(web_ui()));
 
   bool status_has_error = sync_ui_util::GetStatusLabels(
       service, *signin, sync_ui_util::WITH_HTML, &status_label, &link_label) ==
@@ -1406,7 +1419,7 @@ void BrowserOptionsHandler::SetupProxySettingsSection() {
   bool is_extension_controlled = (proxy_config &&
                                   proxy_config->IsExtensionControlled());
 
-  base::FundamentalValue disabled(proxy_prefs_.IsManaged() ||
+  base::FundamentalValue disabled(profile_pref_registrar_.IsManaged() ||
                                   is_extension_controlled);
   base::FundamentalValue extension_controlled(is_extension_controlled);
   web_ui()->CallJavascriptFunction("BrowserOptions.setupProxySettingsSection",