[ci] Run web tests in wasm (unit + integration). (#8111)

Adds CI configuration to run web integration tests (in the master channel) compiled to Wasm.

It also removes the `build-examples` step from web integration tests, in some isolated testing:

| platform tests shard | With build-examples | Without build-examples |
|---|-----|-----|
| 1 | 30m | 21m |
| 2 | 13m | 11m |
| 3 | 17m | 10m |

## Issues

* Fixes https://github.com/flutter/flutter/issues/151664

script/tool/lib/src/dart_test_command.dart

@@ -41,6 +41,8 @@ class DartTestCommand extends PackageLoopingCommand {
       help: 'Runs tests on the given platform instead of the default platform '
           '("vm" in most cases, "chrome" for web plugin implementations).',
     );
+    argParser.addFlag(kWebWasmFlag,
+        help: 'Compile to WebAssembly rather than JavaScript');
   }
 
   static const String _platformFlag = 'platform';
@@ -108,18 +110,21 @@ class DartTestCommand extends PackageLoopingCommand {
       platform = 'chrome';
     }
 
+    // Whether to run web tests compiled to wasm.
+    final bool wasm = platform != 'vm' && getBoolArg(kWebWasmFlag);
+
     bool passed;
     if (package.requiresFlutter()) {
-      passed = await _runFlutterTests(package, platform: platform);
+      passed = await _runFlutterTests(package, platform: platform, wasm: wasm);
     } else {
-      passed = await _runDartTests(package, platform: platform);
+      passed = await _runDartTests(package, platform: platform, wasm: wasm);
     }
     return passed ? PackageResult.success() : PackageResult.fail();
   }
 
   /// Runs the Dart tests for a Flutter package, returning true on success.
   Future<bool> _runFlutterTests(RepositoryPackage package,
-      {String? platform}) async {
+      {String? platform, bool wasm = false}) async {
     final String experiment = getStringArg(kEnableExperiment);
 
     final int exitCode = await processRunner.runAndStream(
@@ -131,6 +136,7 @@ class DartTestCommand extends PackageLoopingCommand {
         // Flutter defaults to VM mode (under a different name) and explicitly
         // setting it is deprecated, so pass nothing in that case.
         if (platform != null && platform != 'vm') '--platform=$platform',
+        if (wasm) '--wasm',
       ],
       workingDir: package.directory,
     );
@@ -139,7 +145,7 @@ class DartTestCommand extends PackageLoopingCommand {
 
   /// Runs the Dart tests for a non-Flutter package, returning true on success.
   Future<bool> _runDartTests(RepositoryPackage package,
-      {String? platform}) async {
+      {String? platform, bool wasm = false}) async {
     // Unlike `flutter test`, `dart run test` does not automatically get
     // packages
     if (!await runPubGet(package, processRunner, super.platform)) {
@@ -156,6 +162,7 @@ class DartTestCommand extends PackageLoopingCommand {
         if (experiment.isNotEmpty) '--enable-experiment=$experiment',
         'test',
         if (platform != null) '--platform=$platform',
+        if (wasm) '--compiler=dart2wasm',
       ],
       workingDir: package.directory,
     );

script/tool/test/dart_test_command_test.dart

@@ -337,6 +337,33 @@ test_on: vm && browser
       );
     });
 
+    test('runs in Chrome (wasm) when requested for Flutter package', () async {
+      final RepositoryPackage package = createFakePackage(
+        'a_package',
+        packagesDir,
+        isFlutter: true,
+        extraFiles: <String>['test/empty_test.dart'],
+      );
+
+      await runCapturingPrint(
+          runner, <String>['dart-test', '--platform=chrome', '--wasm']);
+
+      expect(
+        processRunner.recordedCalls,
+        orderedEquals(<ProcessCall>[
+          ProcessCall(
+              getFlutterCommand(mockPlatform),
+              const <String>[
+                'test',
+                '--color',
+                '--platform=chrome',
+                '--wasm',
+              ],
+              package.path),
+        ]),
+      );
+    });
+
     test('runs in Chrome by default for Flutter plugins that implement web',
         () async {
       final RepositoryPackage plugin = createFakePlugin(
@@ -517,6 +544,33 @@ test_on: vm && browser
       );
     });
 
+    test('runs in Chrome (wasm) when requested for Dart package', () async {
+      final RepositoryPackage package = createFakePackage(
+        'package',
+        packagesDir,
+        extraFiles: <String>['test/empty_test.dart'],
+      );
+
+      await runCapturingPrint(
+          runner, <String>['dart-test', '--platform=chrome', '--wasm']);
+
+      expect(
+        processRunner.recordedCalls,
+        orderedEquals(<ProcessCall>[
+          ProcessCall('dart', const <String>['pub', 'get'], package.path),
+          ProcessCall(
+              'dart',
+              const <String>[
+                'run',
+                'test',
+                '--platform=chrome',
+                '--compiler=dart2wasm',
+              ],
+              package.path),
+        ]),
+      );
+    });
+
     test('skips running in browser mode if package opts out', () async {
       final RepositoryPackage package = createFakePackage(
         'a_package',