Force benchmark app to portrait (#112502)

dev/benchmarks/microbenchmarks/lib/foundation/all_elements_bench.dart

@@ -4,6 +4,7 @@
 
 import 'package:flutter/material.dart';
 import 'package:flutter/scheduler.dart';
+import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart' show collectAllElementsFrom;
 
 import '../common.dart';
@@ -42,6 +43,12 @@ Future<void> main() async {
     ),
   ));
 
+  // Lists may not be scrolled into frame in landscape.
+  SystemChrome.setPreferredOrientations(<DeviceOrientation>[
+    DeviceOrientation.portraitUp,
+    DeviceOrientation.portraitDown,
+  ]);
+
   // Wait for frame rendering to stabilize.
   for (int i = 0; i < 5; i++) {
     await SchedulerBinding.instance.endOfFrame;