OOBE: Hide Guest Mode button if disabled by policy

This cl adds an observer that listens for guest mode policy changes
and show/hides the Guest Mode button.

This only affects the OOBE flow. Non-OOBE Lock screen already hides
Guest Mode button if policy is updated.

Bug:936600

Change-Id: I12f541d22b6877328c2d6351774e620e3c18e166
Reviewed-on: https://chromium-review.googlesource.com/c/1492953
Commit-Queue: Tony De Luna <tonydeluna@chromium.org>
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636889}

chrome/browser/chromeos/login/wizard_controller.cc

@@ -89,6 +89,7 @@
 #include "chrome/browser/policy/profile_policy_connector_factory.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_manager.h"
+#include "chrome/browser/ui/ash/login_screen_client.h"
 #include "chrome/browser/ui/ash/tablet_mode_client.h"
 #include "chrome/browser/ui/webui/chromeos/login/oobe_ui.h"
 #include "chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h"
@@ -332,6 +333,12 @@ void WizardController::Init(OobeScreen first_screen) {
                          weak_factory_.GetWeakPtr()));
     }
   }
+  if (CrosSettings::IsInitialized()) {
+    guest_mode_policy_subscription_ = CrosSettings::Get()->AddSettingsObserver(
+        kAccountsPrefAllowGuest,
+        base::BindRepeating(&WizardController::OnGuestModePolicyUpdated,
+                            weak_factory_.GetWeakPtr()));
+  }
 
   // Use the saved screen preference from Local State.
   const std::string screen_pref =
@@ -1571,6 +1578,11 @@ void WizardController::OnAccessibilityStatusChanged(
   }
 }
 
+void WizardController::OnGuestModePolicyUpdated() {
+  LoginScreenClient::Get()->login_screen()->SetShowGuestButtonInOobe(
+      user_manager::UserManager::Get()->IsGuestSessionAllowed());
+}
+
 void WizardController::AutoLaunchKioskApp() {
   KioskAppManager::App app_data;
   std::string app_id = KioskAppManager::Get()->GetAutoLaunchApp();

chrome/browser/chromeos/login/wizard_controller.h

@@ -279,6 +279,9 @@ class WizardController : public BaseScreenDelegate,
   void OnAccessibilityStatusChanged(
       const AccessibilityStatusEventDetails& details);
 
+  // Notification of Guest Mode policy changes.
+  void OnGuestModePolicyUpdated();
+
   // Switches from one screen to another.
   void SetCurrentScreen(BaseScreen* screen);
 
@@ -421,6 +424,8 @@ class WizardController : public BaseScreenDelegate,
   friend class WizardControllerSupervisionTransitionOobeTest;
 
   std::unique_ptr<AccessibilityStatusSubscription> accessibility_subscription_;
+  std::unique_ptr<CrosSettings::ObserverSubscription>
+      guest_mode_policy_subscription_;
 
   std::unique_ptr<SimpleGeolocationProvider> geolocation_provider_;
   std::unique_ptr<TimeZoneProvider> timezone_provider_;