[Companion] Make notification dialog non-cancelable

Bug: 63405718
Test: Ensute that the notification access dialog is not dismissable with
either back button or touch outside
Change-Id: I613da247a2adc0571478f649a2191cd5840359f0

src/com/android/settings/notification/NotificationAccessConfirmationActivity.java

@@ -82,6 +82,9 @@ public class NotificationAccessConfirmationActivity extends Activity
         AlertController
                 .create(this, this, getWindow())
                 .installContent(p);
+        // Consistent with the permission dialog
+        // Used instead of p.mCancelable as that is only honored for AlertDialog
+        getWindow().setCloseOnTouchOutside(false); 
     }
 
     private void onAllow() {
@@ -108,6 +111,12 @@ public class NotificationAccessConfirmationActivity extends Activity
         return AlertActivity.dispatchPopulateAccessibilityEvent(this, event);
     }
 
+    @Override
+    public void onBackPressed() {
+        // Suppress finishing the activity on back button press,
+        // consistently with the permission dialog behavior
+    }
+
     @Override
     public void cancel() {
         finish();