Ash Display: Do not call PrivacyScreenController observers on init.

Because we display a toast when the privacy screen setting changes,
we do not want to display it on initialization or switching users.

BUG=1040648

Change-Id: I7f507fa401e4c040f8dc3c531a3aaea91e3ff1fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2079799
Commit-Queue: Tim Song <tengs@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Gil Dekel <gildekel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745363}

ash/display/privacy_screen_controller.cc

@@ -90,12 +90,15 @@ void PrivacyScreenController::OnDisplayModeChanged(
   }
 }
 
-void PrivacyScreenController::OnEnabledPrefChanged() {
+void PrivacyScreenController::OnEnabledPrefChanged(bool notify_observers) {
   if (IsSupported()) {
     const bool is_enabled = GetEnabled();
     Shell::Get()->display_configurator()->SetPrivacyScreenOnInternalDisplay(
         is_enabled);
 
+    if (!notify_observers)
+      return;
+
     for (Observer& observer : observers_)
       observer.OnPrivacyScreenSettingChanged(is_enabled);
   }
@@ -109,9 +112,12 @@ void PrivacyScreenController::InitFromUserPrefs() {
   pref_change_registrar_->Add(
       prefs::kDisplayPrivacyScreenEnabled,
       base::BindRepeating(&PrivacyScreenController::OnEnabledPrefChanged,
-                          base::Unretained(this)));
+                          base::Unretained(this),
+                          /*notify_observers=*/true));
 
-  OnEnabledPrefChanged();
+  // We don't want to notify observers upon initialization or on account change
+  // because changes will trigger a toast to show up.
+  OnEnabledPrefChanged(/*notify_observers=*/false);
 }
 
 }  // namespace ash

ash/display/privacy_screen_controller.h

@@ -60,7 +60,7 @@ class ASH_EXPORT PrivacyScreenController
 
  private:
   // Called when the user pref for the status of PrivacyScreen is changed.
-  void OnEnabledPrefChanged();
+  void OnEnabledPrefChanged(bool notify_observers);
 
   // Called when a change to |active_user_pref_service_| is detected (i.e. when
   // OnActiveUserPrefServiceChanged() is called.

ash/display/privacy_screen_controller_unittest.cc

@@ -148,6 +148,9 @@ TEST_F(PrivacyScreenControllerTest, TestEnableAndDisable) {
 
   // Enable for user 1, and switch to user 2. User 2 should have it disabled.
   controller()->SetEnabled(true);
+  // Switching accounts shouldn't trigger observers.
+  ::testing::Mock::VerifyAndClear(observer());
+  EXPECT_CALL(*observer(), OnPrivacyScreenSettingChanged).Times(0);
   EXPECT_TRUE(controller()->GetEnabled());
   SwitchActiveUser(kUser2Email);
   EXPECT_FALSE(controller()->GetEnabled());