Add policy provider that would filter extensions/apps allowed on the

chrome/browser/extensions/extension_system_impl.h

Index: chrome/browser/extensions/extension_system_impl.h
diff --git a/chrome/browser/extensions/extension_system_impl.h b/chrome/browser/extensions/extension_system_impl.h
index 5cd96a310ff1c93fcefe1abbea79f166005cdf8e..236cee2ae8e384f6adb426d47a4db7cd26ac75c9 100644
--- a/chrome/browser/extensions/extension_system_impl.h
+++ b/chrome/browser/extensions/extension_system_impl.h
@@ -15,6 +15,13 @@
 class Profile;
 class ValueStore;
 
+#if defined(OS_CHROMEOS)
+namespace chromeos {
+class DeviceLocalAccountManagementPolicyProvider;
+class SigninScreenPolicyProvider;
+}
+#endif  // defined(OS_CHROMEOS)
+
 namespace extensions {
 
 class ExtensionSystemSharedFactory;
@@ -134,6 +141,8 @@ class ExtensionSystemImpl : public ExtensionSystem {
 #if defined(OS_CHROMEOS)
     std::unique_ptr<chromeos::DeviceLocalAccountManagementPolicyProvider>
         device_local_account_management_policy_provider_;
+    std::unique_ptr<chromeos::SigninScreenPolicyProvider>
+        signin_screen_policy_provider_;
     std::unique_ptr<InstallGate> kiosk_app_update_install_gate_;
 #endif