Bump lower Dart SDK constraints to 3.0 & add class modifiers (#122546)

Bump lower Dart SDK constraints to 3.0 & add class modifiers
diff --git a/dev/automated_tests/pubspec.yaml b/dev/automated_tests/pubspec.yaml
index 843aacb..ddadd9f 100644
--- a/dev/automated_tests/pubspec.yaml
+++ b/dev/automated_tests/pubspec.yaml
@@ -1,7 +1,7 @@
 name: flutter_automated_tests
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/benchmarks/complex_layout/pubspec.yaml b/dev/benchmarks/complex_layout/pubspec.yaml
index b8fb09a..3fc886a 100644
--- a/dev/benchmarks/complex_layout/pubspec.yaml
+++ b/dev/benchmarks/complex_layout/pubspec.yaml
@@ -2,7 +2,7 @@
 description: A benchmark of a relatively complex layout.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/benchmarks/macrobenchmarks/pubspec.yaml b/dev/benchmarks/macrobenchmarks/pubspec.yaml
index b3b7b5d..3897319 100644
--- a/dev/benchmarks/macrobenchmarks/pubspec.yaml
+++ b/dev/benchmarks/macrobenchmarks/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Performance benchmarks using flutter drive.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/benchmarks/microbenchmarks/pubspec.yaml b/dev/benchmarks/microbenchmarks/pubspec.yaml
index c85f6c2..bb0632c 100644
--- a/dev/benchmarks/microbenchmarks/pubspec.yaml
+++ b/dev/benchmarks/microbenchmarks/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Small benchmarks for very specific parts of the Flutter framework.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   meta: 1.9.0
diff --git a/dev/benchmarks/multiple_flutters/module/pubspec.yaml b/dev/benchmarks/multiple_flutters/module/pubspec.yaml
index 4f002a3..2d1b55f 100644
--- a/dev/benchmarks/multiple_flutters/module/pubspec.yaml
+++ b/dev/benchmarks/multiple_flutters/module/pubspec.yaml
@@ -4,7 +4,7 @@
 version: 1.0.0+1
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/benchmarks/platform_channels_benchmarks/pubspec.yaml b/dev/benchmarks/platform_channels_benchmarks/pubspec.yaml
index f6e7cb5..59f2c7e 100644
--- a/dev/benchmarks/platform_channels_benchmarks/pubspec.yaml
+++ b/dev/benchmarks/platform_channels_benchmarks/pubspec.yaml
@@ -5,7 +5,7 @@
 version: 1.0.0+1
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/benchmarks/platform_views_layout/pubspec.yaml b/dev/benchmarks/platform_views_layout/pubspec.yaml
index 2c1fc97..d98f620 100644
--- a/dev/benchmarks/platform_views_layout/pubspec.yaml
+++ b/dev/benchmarks/platform_views_layout/pubspec.yaml
@@ -2,7 +2,7 @@
 description: A benchmark for platform views.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/benchmarks/platform_views_layout_hybrid_composition/pubspec.yaml b/dev/benchmarks/platform_views_layout_hybrid_composition/pubspec.yaml
index e3976ce..9d8846e 100644
--- a/dev/benchmarks/platform_views_layout_hybrid_composition/pubspec.yaml
+++ b/dev/benchmarks/platform_views_layout_hybrid_composition/pubspec.yaml
@@ -2,7 +2,7 @@
 description: A benchmark for platform views, using hybrid composition on android.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/benchmarks/test_apps/stocks/pubspec.yaml b/dev/benchmarks/test_apps/stocks/pubspec.yaml
index 0854fd4..085b185 100644
--- a/dev/benchmarks/test_apps/stocks/pubspec.yaml
+++ b/dev/benchmarks/test_apps/stocks/pubspec.yaml
@@ -1,7 +1,7 @@
 name: stocks
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/bots/pubspec.yaml b/dev/bots/pubspec.yaml
index 2f93585..2433f18 100644
--- a/dev/bots/pubspec.yaml
+++ b/dev/bots/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Scripts which run on bots.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   args: 2.4.0
diff --git a/dev/conductor/core/pubspec.yaml b/dev/conductor/core/pubspec.yaml
index 8626450..c01bc3c 100644
--- a/dev/conductor/core/pubspec.yaml
+++ b/dev/conductor/core/pubspec.yaml
@@ -4,7 +4,7 @@
 publish_to: none
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   archive: 3.3.2
diff --git a/dev/customer_testing/pubspec.yaml b/dev/customer_testing/pubspec.yaml
index 0404e38..54923e5 100644
--- a/dev/customer_testing/pubspec.yaml
+++ b/dev/customer_testing/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Tool to run the tests listed in the flutter/tests repository.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   args: 2.4.0
diff --git a/dev/devicelab/bin/tasks/plugin_dependencies_test.dart b/dev/devicelab/bin/tasks/plugin_dependencies_test.dart
index 86b116f..da77674 100644
--- a/dev/devicelab/bin/tasks/plugin_dependencies_test.dart
+++ b/dev/devicelab/bin/tasks/plugin_dependencies_test.dart
@@ -101,7 +101,7 @@
     sdk: flutter
 
 environment:
-  sdk: ">=2.0.0-dev.28.0 <4.0.0"
+  sdk: '>=3.0.0-0 <4.0.0'
   flutter: ">=1.5.0"
 ''', flush: true);
 
diff --git a/dev/devicelab/pubspec.yaml b/dev/devicelab/pubspec.yaml
index 5383be7..cef944b 100644
--- a/dev/devicelab/pubspec.yaml
+++ b/dev/devicelab/pubspec.yaml
@@ -3,7 +3,7 @@
 homepage: https://github.com/flutter/flutter
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   archive: 3.3.2
diff --git a/dev/integration_tests/deferred_components_test/pubspec.yaml b/dev/integration_tests/deferred_components_test/pubspec.yaml
index 575155d..6b60812 100644
--- a/dev/integration_tests/deferred_components_test/pubspec.yaml
+++ b/dev/integration_tests/deferred_components_test/pubspec.yaml
@@ -3,7 +3,7 @@
 publish_to: 'none'
 version: 1.0.0+1
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/external_ui/pubspec.yaml b/dev/integration_tests/external_ui/pubspec.yaml
index 720f157..9c93fe6 100644
--- a/dev/integration_tests/external_ui/pubspec.yaml
+++ b/dev/integration_tests/external_ui/pubspec.yaml
@@ -2,7 +2,7 @@
 description: A test of Flutter integrating external UIs.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/flavors/pubspec.yaml b/dev/integration_tests/flavors/pubspec.yaml
index 0110643..8880720 100644
--- a/dev/integration_tests/flavors/pubspec.yaml
+++ b/dev/integration_tests/flavors/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Integration test for build flavors.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/flutter_gallery/pubspec.yaml b/dev/integration_tests/flutter_gallery/pubspec.yaml
index 13bae98..08911a3 100644
--- a/dev/integration_tests/flutter_gallery/pubspec.yaml
+++ b/dev/integration_tests/flutter_gallery/pubspec.yaml
@@ -1,7 +1,7 @@
 name: flutter_gallery
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/gradle_deprecated_settings/pubspec.yaml b/dev/integration_tests/gradle_deprecated_settings/pubspec.yaml
index 49d77fd..3093449 100644
--- a/dev/integration_tests/gradle_deprecated_settings/pubspec.yaml
+++ b/dev/integration_tests/gradle_deprecated_settings/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Integration test for the current settings.gradle.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/hybrid_android_views/pubspec.yaml b/dev/integration_tests/hybrid_android_views/pubspec.yaml
index c62f97e..38924a3 100644
--- a/dev/integration_tests/hybrid_android_views/pubspec.yaml
+++ b/dev/integration_tests/hybrid_android_views/pubspec.yaml
@@ -4,7 +4,7 @@
 description: An integration test for hybrid composition on Android
 version: 1.0.0+1
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/ios_add2app_life_cycle/flutterapp/pubspec.yaml b/dev/integration_tests/ios_add2app_life_cycle/flutterapp/pubspec.yaml
index bd4137f..6d88ddc 100644
--- a/dev/integration_tests/ios_add2app_life_cycle/flutterapp/pubspec.yaml
+++ b/dev/integration_tests/ios_add2app_life_cycle/flutterapp/pubspec.yaml
@@ -14,7 +14,7 @@
 version: 1.0.0+1
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/ios_app_with_extensions/pubspec.yaml b/dev/integration_tests/ios_app_with_extensions/pubspec.yaml
index f966323..c3e1c47 100644
--- a/dev/integration_tests/ios_app_with_extensions/pubspec.yaml
+++ b/dev/integration_tests/ios_app_with_extensions/pubspec.yaml
@@ -13,7 +13,7 @@
 version: 1.0.0+1
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/ios_platform_view_tests/pubspec.yaml b/dev/integration_tests/ios_platform_view_tests/pubspec.yaml
index 5d11e15..2272edf 100644
--- a/dev/integration_tests/ios_platform_view_tests/pubspec.yaml
+++ b/dev/integration_tests/ios_platform_view_tests/pubspec.yaml
@@ -3,7 +3,7 @@
 version: 1.0.0+1
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/non_nullable/pubspec.yaml b/dev/integration_tests/non_nullable/pubspec.yaml
index ea21f8e..d4871f0 100644
--- a/dev/integration_tests/non_nullable/pubspec.yaml
+++ b/dev/integration_tests/non_nullable/pubspec.yaml
@@ -5,7 +5,7 @@
 version: 1.0.0+1
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/platform_interaction/pubspec.yaml b/dev/integration_tests/platform_interaction/pubspec.yaml
index 7aec9d6..536f6de 100644
--- a/dev/integration_tests/platform_interaction/pubspec.yaml
+++ b/dev/integration_tests/platform_interaction/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Integration test for platform interactions.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/release_smoke_test/pubspec.yaml b/dev/integration_tests/release_smoke_test/pubspec.yaml
index 99abd80..07fbeb3 100644
--- a/dev/integration_tests/release_smoke_test/pubspec.yaml
+++ b/dev/integration_tests/release_smoke_test/pubspec.yaml
@@ -1,7 +1,7 @@
 name: release_smoke_test
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/spell_check/pubspec.yaml b/dev/integration_tests/spell_check/pubspec.yaml
index a0bd6ac..0950cb2 100644
--- a/dev/integration_tests/spell_check/pubspec.yaml
+++ b/dev/integration_tests/spell_check/pubspec.yaml
@@ -18,7 +18,7 @@
 version: 1.0.0+1
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 # Dependencies specify other packages that your package needs in order to work.
 # To automatically upgrade your package dependencies to the latest versions
diff --git a/dev/integration_tests/ui/pubspec.yaml b/dev/integration_tests/ui/pubspec.yaml
index b8cb947..e79d363 100644
--- a/dev/integration_tests/ui/pubspec.yaml
+++ b/dev/integration_tests/ui/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Flutter non-plugin UI integration tests.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/web/pubspec.yaml b/dev/integration_tests/web/pubspec.yaml
index 8195718..3c053e3 100644
--- a/dev/integration_tests/web/pubspec.yaml
+++ b/dev/integration_tests/web/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Integration test for web compilation.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 flutter:
   assets:
diff --git a/dev/integration_tests/web_compile_tests/pubspec.yaml b/dev/integration_tests/web_compile_tests/pubspec.yaml
index 83ef602..7e18e56 100644
--- a/dev/integration_tests/web_compile_tests/pubspec.yaml
+++ b/dev/integration_tests/web_compile_tests/pubspec.yaml
@@ -1,6 +1,6 @@
 name: web_compile_tests
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/web_e2e_tests/pubspec.yaml b/dev/integration_tests/web_e2e_tests/pubspec.yaml
index e2a7801..5312ae0 100644
--- a/dev/integration_tests/web_e2e_tests/pubspec.yaml
+++ b/dev/integration_tests/web_e2e_tests/pubspec.yaml
@@ -2,7 +2,7 @@
 publish_to: none
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 flutter:
   assets:
diff --git a/dev/integration_tests/wide_gamut_test/pubspec.yaml b/dev/integration_tests/wide_gamut_test/pubspec.yaml
index a35963a..c0044d12 100644
--- a/dev/integration_tests/wide_gamut_test/pubspec.yaml
+++ b/dev/integration_tests/wide_gamut_test/pubspec.yaml
@@ -5,7 +5,7 @@
 version: 1.0.0+1
 
 environment:
-  sdk: '>=3.0.0-157.0.dev <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/windows_startup_test/pubspec.yaml b/dev/integration_tests/windows_startup_test/pubspec.yaml
index ab5450c..eb0e639 100644
--- a/dev/integration_tests/windows_startup_test/pubspec.yaml
+++ b/dev/integration_tests/windows_startup_test/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Integration test for Windows app's startup.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/manual_tests/pubspec.yaml b/dev/manual_tests/pubspec.yaml
index c18a933..24c1ffd 100644
--- a/dev/manual_tests/pubspec.yaml
+++ b/dev/manual_tests/pubspec.yaml
@@ -1,7 +1,7 @@
 name: manual_tests
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/missing_dependency_tests/pubspec.yaml b/dev/missing_dependency_tests/pubspec.yaml
index 5dda1d8..a322c18 100644
--- a/dev/missing_dependency_tests/pubspec.yaml
+++ b/dev/missing_dependency_tests/pubspec.yaml
@@ -1,7 +1,7 @@
 name: missing_dependency_tests
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/tools/dartdoc.dart b/dev/tools/dartdoc.dart
index b3ea776..8bf6c48 100644
--- a/dev/tools/dartdoc.dart
+++ b/dev/tools/dartdoc.dart
@@ -59,7 +59,7 @@
   buf.writeln('homepage: https://flutter.dev');
   buf.writeln('version: 0.0.0');
   buf.writeln('environment:');
-  buf.writeln("  sdk: '>=2.19.0 <4.0.0'");
+  buf.writeln("  sdk: '>=3.0.0-0 <4.0.0'");
   buf.writeln('dependencies:');
   for (final String package in findPackageNames()) {
     buf.writeln('  $package:');
diff --git a/dev/tools/gen_defaults/pubspec.yaml b/dev/tools/gen_defaults/pubspec.yaml
index 3d850f0..9c4c421 100644
--- a/dev/tools/gen_defaults/pubspec.yaml
+++ b/dev/tools/gen_defaults/pubspec.yaml
@@ -3,7 +3,7 @@
 version: 1.0.0
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
 
diff --git a/dev/tools/gen_keycodes/pubspec.yaml b/dev/tools/gen_keycodes/pubspec.yaml
index 861c783..2162499 100644
--- a/dev/tools/gen_keycodes/pubspec.yaml
+++ b/dev/tools/gen_keycodes/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Generates keycode source files from various resources.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   args: 2.4.0
diff --git a/dev/tools/pubspec.yaml b/dev/tools/pubspec.yaml
index cfa0366..3db47df 100644
--- a/dev/tools/pubspec.yaml
+++ b/dev/tools/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Various repository development tools for flutter.
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   archive: 3.3.2
diff --git a/dev/tools/vitool/pubspec.yaml b/dev/tools/vitool/pubspec.yaml
index 99670d5..38ec905 100644
--- a/dev/tools/vitool/pubspec.yaml
+++ b/dev/tools/vitool/pubspec.yaml
@@ -4,7 +4,7 @@
 homepage: https://flutter.dev
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter:
diff --git a/dev/tracing_tests/pubspec.yaml b/dev/tracing_tests/pubspec.yaml
index aaf8e88..df98482 100644
--- a/dev/tracing_tests/pubspec.yaml
+++ b/dev/tracing_tests/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Various tests for tracing in flutter/flutter
 
 environment:
-  sdk: '>=2.19.0-0 <4.0.0'
+  sdk: '>=3.0.0-0 <4.0.0'
 
 dependencies:
   flutter: