[CP] Migrate web-only initialization APIs (#133891)

This CP lands PR https://github.com/flutter/flutter/pull/129856 into `stable`.

The PR above was part of a engine+framework change that got split in half during the stable cut, so now users are seeing some warnings that they can't act on.

(Those warnings were only intended for people who were using our methods manually, rather than using normal flutter tooling).

## Issues

Fixes https://github.com/flutter/flutter/issues/133069

packages/flutter/lib/src/foundation/_platform_web.dart

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui' as ui;
+import 'dart:ui_web' as ui_web;
 
 import '../services/dom.dart';
 
@@ -23,9 +23,7 @@ platform.TargetPlatform get defaultTargetPlatform {
 final platform.TargetPlatform? _testPlatform = () {
   platform.TargetPlatform? result;
   assert(() {
-    // This member is only available in the web's dart:ui implementation.
-    // ignore: undefined_prefixed_name
-    if (ui.debugEmulateFlutterTesterEnvironment as bool) {
+    if (ui_web.debugEmulateFlutterTesterEnvironment) {
       result = platform.TargetPlatform.android;
     }
     return true;

packages/flutter_tools/lib/src/web/bootstrap.dart

@@ -219,6 +219,7 @@ String generateTestEntrypoint({
   // @dart = ${languageVersion.major}.${languageVersion.minor}
   import 'org-dartlang-app:///$relativeTestPath' as test;
   import 'dart:ui' as ui;
+  import 'dart:ui_web' as ui_web;
   import 'dart:html';
   import 'dart:js';
   ${testConfigPath != null ? "import '${Uri.file(testConfigPath)}' as test_config;" : ""}
@@ -227,7 +228,7 @@ String generateTestEntrypoint({
   import 'package:test_api/backend.dart';
 
   Future<void> main() async {
-    ui.debugEmulateFlutterTesterEnvironment = true;
+    ui_web.debugEmulateFlutterTesterEnvironment = true;
     await ui.webOnlyInitializePlatform();
     webGoldenComparator = DefaultWebGoldenComparator(Uri.parse('${Uri.file(absolutePath)}'));
     (ui.window as dynamic).debugOverrideDevicePixelRatio(3.0);

packages/flutter_tools/lib/src/web/file_generators/main_dart.dart

@@ -19,7 +19,7 @@ String generateMainDartFile(String appEntrypoint, {
     '',
     '// ignore_for_file: type=lint',
     '',
-    "import 'dart:ui' as ui;",
+    "import 'dart:ui_web' as ui_web;",
     "import 'dart:async';",
     '',
     "import '$appEntrypoint' as entrypoint;",
@@ -29,7 +29,7 @@ String generateMainDartFile(String appEntrypoint, {
     'typedef _NullaryFunction = dynamic Function();',
     '',
     'Future<void> main() async {',
-    '  await ui.webOnlyWarmupEngine(',
+    '  await ui_web.bootstrapEngine(',
     '    runApp: () {',
     '      if (entrypoint.main is _UnaryFunction) {',
     '        return (entrypoint.main as _UnaryFunction)(<String>[]);',

packages/flutter_tools/test/general.shard/build_system/targets/web_test.dart

@@ -118,7 +118,7 @@ void main() {
     expect(generated, contains("import 'package:foo/main.dart' as entrypoint;"));
 
     // Main
-    expect(generated, contains('ui.webOnlyWarmupEngine('));
+    expect(generated, contains('ui_web.bootstrapEngine('));
     expect(generated, contains('entrypoint.main as _'));
   }, overrides: <Type, Generator>{
     TemplateRenderer: () => const MustacheTemplateRenderer(),
@@ -270,7 +270,7 @@ void main() {
     expect(generated, contains("import 'package:foo/main.dart' as entrypoint;"));
 
     // Main
-    expect(generated, contains('ui.webOnlyWarmupEngine('));
+    expect(generated, contains('ui_web.bootstrapEngine('));
     expect(generated, contains('entrypoint.main as _'));
   }, overrides: <Type, Generator>{
     Platform: () => windows,
@@ -295,7 +295,7 @@ void main() {
     expect(generated, contains("import 'package:foo/main.dart' as entrypoint;"));
 
     // Main
-    expect(generated, contains('ui.webOnlyWarmupEngine('));
+    expect(generated, contains('ui_web.bootstrapEngine('));
     expect(generated, contains('entrypoint.main as _'));
   }, overrides: <Type, Generator>{
     TemplateRenderer: () => const MustacheTemplateRenderer(),
@@ -351,7 +351,7 @@ void main() {
     expect(generated, contains("import 'package:foo/main.dart' as entrypoint;"));
 
     // Main
-    expect(generated, contains('ui.webOnlyWarmupEngine('));
+    expect(generated, contains('ui_web.bootstrapEngine('));
     expect(generated, contains('entrypoint.main as _'));
   }, overrides: <Type, Generator>{
     TemplateRenderer: () => const MustacheTemplateRenderer(),

packages/flutter_tools/test/general.shard/resident_web_runner_test.dart

@@ -730,8 +730,8 @@ void main() {
     final String entrypointContents =
         fileSystem.file(webDevFS.mainUri).readAsStringSync();
     expect(entrypointContents, contains('// Flutter web bootstrap script'));
-    expect(entrypointContents, contains("import 'dart:ui' as ui;"));
-    expect(entrypointContents, contains('await ui.webOnlyWarmupEngine('));
+    expect(entrypointContents, contains("import 'dart:ui_web' as ui_web;"));
+    expect(entrypointContents, contains('await ui_web.bootstrapEngine('));
 
     expect(logger.statusText, contains('Restarted application in'));
     expect(result.code, 0);

packages/flutter_web_plugins/lib/src/plugin_registry.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 import 'dart:ui' as ui;
+import 'dart:ui_web' as ui_web;
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart';
@@ -57,13 +58,11 @@ class Registrar extends BinaryMessenger {
   /// previously-registered handler and replaces it with the handler
   /// from this object.
   ///
-  /// This method uses a function called `webOnlySetPluginHandler` in
-  /// the [dart:ui] library. That function is only available when
+  /// This method uses a function called `setPluginHandler` in
+  /// the [dart:ui_web] library. That function is only available when
   /// compiling for the web.
   void registerMessageHandler() {
-    // The `ui.webOnlySetPluginHandler` function below is only defined in the Web dart:ui.
-    // ignore: undefined_function, avoid_dynamic_calls
-    ui.webOnlySetPluginHandler(handleFrameworkMessage);
+    ui_web.setPluginHandler(handleFrameworkMessage);
   }
 
   /// Receives a platform message from the framework.
@@ -101,7 +100,7 @@ class Registrar extends BinaryMessenger {
   /// the following:
   ///
   /// ```dart
-  /// ui.webOnlySetPluginHandler(webPluginRegistrar.handleFrameworkMessage);
+  /// ui_web.setPluginHandler(handleFrameworkMessage);
   /// ```
   Future<void> handleFrameworkMessage(
     String channel,

packages/flutter_web_plugins/test/plugin_event_channel_test.dart

@@ -6,7 +6,7 @@
 library;
 
 import 'dart:async';
-import 'dart:ui' as ui;
+import 'dart:ui_web' as ui_web;
 
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -14,7 +14,7 @@ import 'package:flutter_web_plugins/flutter_web_plugins.dart';
 
 void main() {
   // Disabling tester emulation because this test relies on real message channel communication.
-  ui.debugEmulateFlutterTesterEnvironment = false; // ignore: undefined_prefixed_name
+  ui_web.debugEmulateFlutterTesterEnvironment = false;
 
   group('Plugin Event Channel', () {
     setUp(() {

packages/flutter_web_plugins/test/plugin_registry_test.dart

@@ -5,7 +5,7 @@
 @TestOn('chrome') // Uses web-only Flutter SDK
 library;
 
-import 'dart:ui' as ui;
+import 'dart:ui_web' as ui_web;
 
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -31,7 +31,7 @@ class TestPlugin {
 
 void main() {
   // Disabling tester emulation because this test relies on real message channel communication.
-  ui.debugEmulateFlutterTesterEnvironment = false; // ignore: undefined_prefixed_name
+  ui_web.debugEmulateFlutterTesterEnvironment = false;
 
   group('Plugin Registry', () {
     setUp(() {