diff --git a/dev/bots/test.dart b/dev/bots/test.dart
index 1e240c3..e41a6e1 100644
--- a/dev/bots/test.dart
+++ b/dev/bots/test.dart
@@ -912,6 +912,7 @@
       '--driver=test_driver/transitions_perf_e2e_test.dart',
       '--target=test_driver/transitions_perf_e2e.dart',
       '--browser-name=chrome',
+      '--no-sound-null-safety',
       '-d',
       'web-server',
       '--$buildMode',
diff --git a/dev/integration_tests/flutter_gallery/test_driver/run_demos.dart b/dev/integration_tests/flutter_gallery/test_driver/run_demos.dart
index 2df9fab..5f465fc 100644
--- a/dev/integration_tests/flutter_gallery/test_driver/run_demos.dart
+++ b/dev/integration_tests/flutter_gallery/test_driver/run_demos.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'dart:ui';
 
 import 'package:flutter/cupertino.dart';
diff --git a/dev/integration_tests/flutter_gallery/test_driver/scroll_perf.dart b/dev/integration_tests/flutter_gallery/test_driver/scroll_perf.dart
index a82bc68..4440370 100644
--- a/dev/integration_tests/flutter_gallery/test_driver/scroll_perf.dart
+++ b/dev/integration_tests/flutter_gallery/test_driver/scroll_perf.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'package:flutter_driver/driver_extension.dart';
 import 'package:flutter_gallery/gallery/app.dart' show GalleryApp;
 import 'package:flutter/material.dart';
diff --git a/dev/integration_tests/flutter_gallery/test_driver/scroll_perf_test.dart b/dev/integration_tests/flutter_gallery/test_driver/scroll_perf_test.dart
index 668db67..9e6c1e2 100644
--- a/dev/integration_tests/flutter_gallery/test_driver/scroll_perf_test.dart
+++ b/dev/integration_tests/flutter_gallery/test_driver/scroll_perf_test.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'package:flutter_driver/flutter_driver.dart';
 import 'package:test/test.dart' hide TypeMatcher, isInstanceOf;
 
diff --git a/dev/integration_tests/flutter_gallery/test_driver/scroll_perf_web.dart b/dev/integration_tests/flutter_gallery/test_driver/scroll_perf_web.dart
index 1df1be8..ffdaed6 100644
--- a/dev/integration_tests/flutter_gallery/test_driver/scroll_perf_web.dart
+++ b/dev/integration_tests/flutter_gallery/test_driver/scroll_perf_web.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'package:flutter_driver/driver_extension.dart';
 import 'package:flutter_gallery/gallery/app.dart' show GalleryApp;
 import 'package:flutter/material.dart';
diff --git a/dev/integration_tests/flutter_gallery/test_driver/scroll_perf_web_test.dart b/dev/integration_tests/flutter_gallery/test_driver/scroll_perf_web_test.dart
index a71ef59..528f334 100644
--- a/dev/integration_tests/flutter_gallery/test_driver/scroll_perf_web_test.dart
+++ b/dev/integration_tests/flutter_gallery/test_driver/scroll_perf_web_test.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'package:flutter_driver/flutter_driver.dart';
 import 'package:test/test.dart' hide TypeMatcher, isInstanceOf;
 
diff --git a/dev/integration_tests/flutter_gallery/test_driver/transitions_perf.dart b/dev/integration_tests/flutter_gallery/test_driver/transitions_perf.dart
index b4e7e64..ae88a38 100644
--- a/dev/integration_tests/flutter_gallery/test_driver/transitions_perf.dart
+++ b/dev/integration_tests/flutter_gallery/test_driver/transitions_perf.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'dart:convert' show JsonEncoder;
 
 import 'package:flutter_driver/driver_extension.dart';
diff --git a/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_e2e.dart b/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_e2e.dart
index d1f6c4f..2125517 100644
--- a/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_e2e.dart
+++ b/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_e2e.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
diff --git a/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_e2e_test.dart b/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_e2e_test.dart
index d931eff..1d2eeec 100644
--- a/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_e2e_test.dart
+++ b/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_e2e_test.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'package:integration_test/integration_test_driver.dart' as driver;
 
 Future<void> main() => driver.integrationDriver(
diff --git a/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_e2e_with_semantics.dart b/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_e2e_with_semantics.dart
index 1f26cbd..e30850d 100644
--- a/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_e2e_with_semantics.dart
+++ b/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_e2e_with_semantics.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'transitions_perf_e2e.dart' as transitions_perf;
 
 void main() {
diff --git a/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_hybrid_test.dart b/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_hybrid_test.dart
index dc5ab42..572a03b 100644
--- a/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_hybrid_test.dart
+++ b/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_hybrid_test.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'transitions_perf_test.dart' as transitions_perf_test;
 
 void main([List<String> args = const <String>[]]) => transitions_perf_test.main(
diff --git a/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_test.dart b/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_test.dart
index 7cf23b0..ea97a6f 100644
--- a/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_test.dart
+++ b/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_test.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'dart:convert' show JsonEncoder, json;
 
 import 'package:file/file.dart';
diff --git a/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_with_semantics_test.dart b/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_with_semantics_test.dart
index eaa0ca2..40c924b 100644
--- a/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_with_semantics_test.dart
+++ b/dev/integration_tests/flutter_gallery/test_driver/transitions_perf_with_semantics_test.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'transitions_perf_test.dart' as transitions_perf_test;
 
 void main() {
diff --git a/dev/integration_tests/flutter_gallery/test_memory/back_button.dart b/dev/integration_tests/flutter_gallery/test_memory/back_button.dart
index 140a45a..79914614 100644
--- a/dev/integration_tests/flutter_gallery/test_memory/back_button.dart
+++ b/dev/integration_tests/flutter_gallery/test_memory/back_button.dart
@@ -4,6 +4,7 @@
 
 // See //dev/devicelab/bin/tasks/flutter_gallery__memory_nav.dart
 
+// @dart = 2.9
 import 'package:flutter/material.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter_gallery/gallery/app.dart' show GalleryApp;
diff --git a/dev/integration_tests/flutter_gallery/test_memory/image_cache_memory.dart b/dev/integration_tests/flutter_gallery/test_memory/image_cache_memory.dart
index df8eb3b..8ef468f 100644
--- a/dev/integration_tests/flutter_gallery/test_memory/image_cache_memory.dart
+++ b/dev/integration_tests/flutter_gallery/test_memory/image_cache_memory.dart
@@ -4,6 +4,7 @@
 
 // See //dev/devicelab/bin/tasks/flutter_gallery__image_cache_memory.dart
 
+// @dart = 2.9
 import 'package:flutter/widgets.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter_test/flutter_test.dart';
diff --git a/dev/integration_tests/flutter_gallery/test_memory/memory_nav.dart b/dev/integration_tests/flutter_gallery/test_memory/memory_nav.dart
index 5bfd47c..df20344 100644
--- a/dev/integration_tests/flutter_gallery/test_memory/memory_nav.dart
+++ b/dev/integration_tests/flutter_gallery/test_memory/memory_nav.dart
@@ -4,6 +4,7 @@
 
 // See //dev/devicelab/bin/tasks/flutter_gallery__memory_nav.dart
 
+// @dart = 2.9
 import 'dart:async';
 
 import 'package:flutter/material.dart';
diff --git a/dev/integration_tests/web_e2e_tests/test_driver/text_editing_integration.dart b/dev/integration_tests/web_e2e_tests/test_driver/text_editing_integration.dart
index 3c6633d..4524899 100644
--- a/dev/integration_tests/web_e2e_tests/test_driver/text_editing_integration.dart
+++ b/dev/integration_tests/web_e2e_tests/test_driver/text_editing_integration.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'dart:html';
 import 'dart:js_util' as js_util;
 import 'package:flutter/gestures.dart';
diff --git a/dev/integration_tests/web_e2e_tests/test_driver/text_editing_integration_test.dart b/dev/integration_tests/web_e2e_tests/test_driver/text_editing_integration_test.dart
index b2d2a17..94f9938 100644
--- a/dev/integration_tests/web_e2e_tests/test_driver/text_editing_integration_test.dart
+++ b/dev/integration_tests/web_e2e_tests/test_driver/text_editing_integration_test.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'package:integration_test/integration_test_driver.dart' as test;
 
 Future<void> main() async => test.integrationDriver();