Pass --local-engine* from dev/bots/test.dart to `pub test` (only web) (#83308)

This is bassically reapplying #71721, but only enables it on web tests.

There are known issues that several tests under the `integration.shard`
depend on a specific platform, and as a result they require some
additional flexiblity (bots need to build more than one engine, and the
test flags should allow for secondary engines to be picked by such
tests).

By enabling this on the web-test shard, we will reduce the false
positives in the dart-flutter-HHH-web bot.

Fixing the more general problem is tracked by #72368.

dev/bots/test.dart

@@ -54,6 +54,10 @@ final String flutterTester = path.join(flutterRoot, 'bin', 'cache', 'artifacts',
 /// configuration) -- prefilled with the arguments passed to test.dart.
 final List<String> flutterTestArgs = <String>[];
 
+/// Environment variables to override the local engine when running `pub test`,
+/// if such flags are provided to `test.dart`.
+final Map<String,String> localEngineEnv = <String, String>{};
+
 final bool useFlutterTestFormatter = Platform.environment['FLUTTER_TEST_FORMATTER'] == 'true';
 
 const String kShardKey = 'SHARD';
@@ -95,6 +99,12 @@ Future<void> main(List<String> args) async {
   print('$clock STARTING ANALYSIS');
   try {
     flutterTestArgs.addAll(args);
+    for (final String arg in args) {
+      if (arg.startsWith('--local-engine='))
+        localEngineEnv['FLUTTER_LOCAL_ENGINE'] = arg.substring('--local-engine='.length);
+      if (arg.startsWith('--local-engine-src-path='))
+        localEngineEnv['FLUTTER_LOCAL_ENGINE_SRC_PATH'] = arg.substring('--local-engine-src-path='.length);
+    }
     if (Platform.environment.containsKey(CIRRUS_TASK_NAME))
       print('Running task: ${Platform.environment[CIRRUS_TASK_NAME]}');
     print('═' * 80);
@@ -283,6 +293,7 @@ Future<void> _runWebToolTests() async {
     testPaths: <String>[path.join('test', 'web.shard')],
     enableFlutterToolAsserts: true,
     perTestTimeout: const Duration(minutes: 3),
+    includeLocalEngineEnv: true,
   );
 }
 
@@ -1273,6 +1284,11 @@ Future<void> _runFlutterWebTest(String workingDirectory, List<String> tests) asy
   );
 }
 
+// TODO(sigmund): includeLocalEngineEnv should default to true. Currently we
+// only enable it on flutter-web test because some test suites do not work
+// properly when overriding the local engine (for example, because some platform
+// dependent targets are only built on some engines).
+// See https://github.com/flutter/flutter/issues/72368
 Future<void> _pubRunTest(String workingDirectory, {
   List<String> testPaths,
   bool enableFlutterToolAsserts = true,
@@ -1280,6 +1296,7 @@ Future<void> _pubRunTest(String workingDirectory, {
   String coverage,
   bool forceSingleCore = false,
   Duration perTestTimeout,
+  bool includeLocalEngineEnv = false,
 }) async {
   int cpus;
   final String cpuVariable = Platform.environment['CPU']; // CPU is set in cirrus.yml
@@ -1319,6 +1336,7 @@ Future<void> _pubRunTest(String workingDirectory, {
   ];
   final Map<String, String> pubEnvironment = <String, String>{
     'FLUTTER_ROOT': flutterRoot,
+    if (includeLocalEngineEnv) ...localEngineEnv,
   };
   if (Directory(pubCache).existsSync()) {
     pubEnvironment['PUB_CACHE'] = pubCache;