Add missing io import to complex_layout_semantics_perf (#79421)

diff --git a/dev/devicelab/bin/tasks/complex_layout_semantics_perf.dart b/dev/devicelab/bin/tasks/complex_layout_semantics_perf.dart
index b6a97bc..0880d9e 100644
--- a/dev/devicelab/bin/tasks/complex_layout_semantics_perf.dart
+++ b/dev/devicelab/bin/tasks/complex_layout_semantics_perf.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:io';
+
 import 'package:flutter_devicelab/framework/adb.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/framework/host_agent.dart';