Do not call setQuietModeEnabled from the main thread

Call into startUserInBackgroundWithListener->onBeforeStartUser sometimes
can be blocked for a long time if there is an ongoing dexopt operation.

Instead call it from bg thread.

Test: manual
Bug: 72692931
Change-Id: I872c3a2baf6e5ff95aab186f7a8008afec7533d6

services/core/java/com/android/server/pm/UserManagerService.java

@@ -88,6 +88,7 @@ import com.android.internal.annotations.GuardedBy;
 import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.app.IAppOpsService;
 import com.android.internal.logging.MetricsLogger;
+import com.android.internal.os.BackgroundThread;
 import com.android.internal.util.DumpUtils;
 import com.android.internal.util.FastXmlSerializer;
 import com.android.internal.util.Preconditions;
@@ -387,7 +388,9 @@ public class UserManagerService extends IUserManager.Stub {
             }
             final IntentSender target = intent.getParcelableExtra(Intent.EXTRA_INTENT);
             final int userHandle = intent.getIntExtra(Intent.EXTRA_USER_ID, UserHandle.USER_NULL);
-            setQuietModeEnabled(userHandle, false, target);
+            // Call setQuietModeEnabled on bg thread to avoid ANR
+            BackgroundThread.getHandler()
+                    .post(() -> setQuietModeEnabled(userHandle, false, target));
         }
     };