Add a SigninAllowed policy.

chrome/browser/ui/webui/ntp/new_tab_page_sync_handler.cc

Index: chrome/browser/ui/webui/ntp/new_tab_page_sync_handler.cc
diff --git a/chrome/browser/ui/webui/ntp/new_tab_page_sync_handler.cc b/chrome/browser/ui/webui/ntp/new_tab_page_sync_handler.cc
index 1639456ab7727a0d564b74bfd1efda5697a3aec4..c5eeaf110c778fc4ea7308265d76d8d31aa2e41c 100644
--- a/chrome/browser/ui/webui/ntp/new_tab_page_sync_handler.cc
+++ b/chrome/browser/ui/webui/ntp/new_tab_page_sync_handler.cc
@@ -89,9 +89,14 @@ void NewTabPageSyncHandler::HideSyncStatusSection() {
 
 void NewTabPageSyncHandler::BuildAndSendSyncStatus() {
   DCHECK(!waiting_for_initial_page_load_);
+  SigninManager* signin = SigninManagerFactory::GetForProfile(
+      Profile::FromWebUI(web_ui()));
 
   // Hide the sync status section if sync is managed or disabled entirely.
-  if (!sync_service_ || sync_service_->IsManaged()) {
+  if (!sync_service_ ||
+      sync_service_->IsManaged() ||
+      !signin ||
+      !signin->IsSigninAllowed()) {
     HideSyncStatusSection();
     return;
   }
@@ -109,8 +114,6 @@ void NewTabPageSyncHandler::BuildAndSendSyncStatus() {
   //               message).
   string16 status_msg;
   string16 link_text;
-  SigninManager* signin = SigninManagerFactory::GetForProfile(
-      Profile::FromWebUI(web_ui()));
 
   sync_ui_util::MessageType type =
       sync_ui_util::GetStatusLabelsForNewTabPage(sync_service_,
@@ -152,6 +155,13 @@ void NewTabPageSyncHandler::OnStateChanged() {
   BuildAndSendSyncStatus();
 }
 
+void NewTabPageSyncHandler::OnSigninAllowedPrefChange(bool signin_allowed) {
+  // Don't do anything if the page has not yet loaded.
+  if (waiting_for_initial_page_load_)
+    return;
+  BuildAndSendSyncStatus();
+}
+
 void NewTabPageSyncHandler::SendSyncMessageToPage(
     MessageType type, std::string msg,
     std::string linktext) {