Add a SigninAllowed policy.

chrome/browser/ui/browser_command_controller.h

Index: chrome/browser/ui/browser_command_controller.h
diff --git a/chrome/browser/ui/browser_command_controller.h b/chrome/browser/ui/browser_command_controller.h
index 543b841b73481d76fa6779bbfb1f3f699f7180c5..b9b143665a6d642a5829a3a53c6425f4cc59eb85 100644
--- a/chrome/browser/ui/browser_command_controller.h
+++ b/chrome/browser/ui/browser_command_controller.h
@@ -6,7 +6,7 @@
 #define CHROME_BROWSER_UI_BROWSER_COMMAND_CONTROLLER_H_
 
 #include "base/prefs/public/pref_change_registrar.h"
-#include "chrome/browser/api/sync/profile_sync_service_observer.h"
+#include "base/prefs/public/pref_member.h"
 #include "chrome/browser/command_updater.h"
 #include "chrome/browser/command_updater_delegate.h"
 #include "chrome/browser/profiles/profile_info_cache_observer.h"
@@ -169,9 +169,15 @@ class BrowserCommandController : public CommandUpdaterDelegate,
   // Updates the printing command state.
   void UpdatePrintingState();
 
+  // Updates the SHOW_SYNC_SETUP menu entry.
+  void OnSigninAllowedPrefChange();
+
   // Updates the save-page-as command state.
   void UpdateSaveAsState();
 
+  // Updates the show-sync command state.
+  void UpdateShowSyncState(bool show_main_ui);
+
   // Ask the Reload/Stop button to change its icon, and update the Stop command
   // state.  |is_loading| is true if the current WebContents is loading.
   // |force| is true if the button should change its icon immediately.
@@ -207,6 +213,7 @@ class BrowserCommandController : public CommandUpdaterDelegate,
   content::NotificationRegistrar registrar_;
   PrefChangeRegistrar profile_pref_registrar_;
   PrefChangeRegistrar local_pref_registrar_;
+  BooleanPrefMember pref_signin_allowed_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserCommandController);
 };