Hide private DNS settings UI in Guest mode

Hide private DNS settings UI in Guest mode to prevent guest
users modifying global private DNS settings.

Bug: 206987762
Test: 1. make RunSettingsRoboTests \
         ROBOTEST_FILTER=PrivateDnsPreferenceControllerTest
      2. Switch to Guest user and check if the private DNS UI is
         hidden or not.
Change-Id: Iebfb8684da3be32110decd9e8447dd07b1c40387

src/com/android/settings/network/PrivateDnsPreferenceController.java

@@ -84,9 +84,12 @@ public class PrivateDnsPreferenceController extends BasePreferenceController
 
     @Override
     public int getAvailabilityStatus() {
-        return mContext.getResources().getBoolean(R.bool.config_show_private_dns_settings)
+        if (!mContext.getResources().getBoolean(R.bool.config_show_private_dns_settings)) {
-                ? AVAILABLE
+            return UNSUPPORTED_ON_DEVICE;
-                : UNSUPPORTED_ON_DEVICE;
+        }
+        final UserManager userManager = mContext.getSystemService(UserManager.class);
+        if (userManager.isGuestUser()) return DISABLED_FOR_USER;
+        return AVAILABLE;
     }
 
     @Override

tests/robotests/src/com/android/settings/network/PrivateDnsPreferenceControllerTest.java

@@ -27,6 +27,7 @@ import static androidx.lifecycle.Lifecycle.Event.ON_START;
 import static androidx.lifecycle.Lifecycle.Event.ON_STOP;
 
 import static com.android.settings.core.BasePreferenceController.AVAILABLE;
+import static com.android.settings.core.BasePreferenceController.DISABLED_FOR_USER;
 import static com.android.settings.core.BasePreferenceController.UNSUPPORTED_ON_DEVICE;
 
 import static com.google.common.truth.Truth.assertThat;
@@ -36,6 +37,7 @@ import static org.mockito.ArgumentMatchers.nullable;
 import static org.mockito.Mockito.CALLS_REAL_METHODS;
 import static org.mockito.Mockito.atLeastOnce;
 import static org.mockito.Mockito.doNothing;
+import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.reset;
 import static org.mockito.Mockito.spy;
@@ -109,6 +111,8 @@ public class PrivateDnsPreferenceControllerTest {
     private Network mNetwork;
     @Mock
     private Preference mPreference;
+    @Mock
+    private UserManager mUserManager;
     @Captor
     private ArgumentCaptor<NetworkCallback> mCallbackCaptor;
     private PrivateDnsPreferenceController mController;
@@ -127,6 +131,7 @@ public class PrivateDnsPreferenceControllerTest {
         mShadowContentResolver = Shadow.extract(mContentResolver);
         when(mContext.getSystemService(Context.CONNECTIVITY_SERVICE))
                 .thenReturn(mConnectivityManager);
+        when(mContext.getSystemService(UserManager.class)).thenReturn(mUserManager);
         doNothing().when(mConnectivityManager).registerDefaultNetworkCallback(
                 mCallbackCaptor.capture(), nullable(Handler.class));
 
@@ -173,6 +178,12 @@ public class PrivateDnsPreferenceControllerTest {
         assertThat(mController.getAvailabilityStatus()).isEqualTo(UNSUPPORTED_ON_DEVICE);
     }
 
+    @Test
+    public void getAvailabilityStatus_disabledForGuestUser() {
+        doReturn(true).when(mUserManager).isGuestUser();
+        assertThat(mController.getAvailabilityStatus()).isEqualTo(DISABLED_FOR_USER);
+    }
+
     @Test
     public void goThroughLifecycle_shouldRegisterUnregisterSettingsObserver() {
         mLifecycle.handleLifecycleEvent(ON_START);