Update `dev/bots/test.dart` (and friends) to provide `--local-engine-host`. (#132354)

Partial work towards https://github.com/flutter/flutter/issues/132245.

As far as I can tell, this just plumbs flags downwards and has no
semantic changes.

dev/bots/test.dart

@@ -213,7 +213,7 @@ String get shuffleSeed {
 ///
 /// Examples:
 /// SHARD=tool_tests bin/cache/dart-sdk/bin/dart dev/bots/test.dart
-/// bin/cache/dart-sdk/bin/dart dev/bots/test.dart --local-engine=host_debug_unopt
+/// bin/cache/dart-sdk/bin/dart dev/bots/test.dart --local-engine=host_debug_unopt --local-engine-host=host_debug_unopt
 Future<void> main(List<String> args) async {
   try {
     printProgress('STARTING ANALYSIS');
@@ -221,6 +221,9 @@ Future<void> main(List<String> args) async {
       if (arg.startsWith('--local-engine=')) {
         localEngineEnv['FLUTTER_LOCAL_ENGINE'] = arg.substring('--local-engine='.length);
         flutterTestArgs.add(arg);
+      } else if (arg.startsWith('--local-engine-host=')) {
+        localEngineEnv['FLUTTER_LOCAL_ENGINE_HOST'] = arg.substring('--local-engine-host='.length);
+        flutterTestArgs.add(arg);
       } else if (arg.startsWith('--local-engine-src-path=')) {
         localEngineEnv['FLUTTER_LOCAL_ENGINE_SRC_PATH'] = arg.substring('--local-engine-src-path='.length);
         flutterTestArgs.add(arg);

packages/flutter_tools/README.md

@@ -67,14 +67,16 @@ Please avoid setting any other timeouts.
 #### Using local engine builds in integration tests
 
 The integration tests can be configured to use a specific local engine
-variant by setting the `FLUTTER_LOCAL_ENGINE` environment variable to the
-name of the local engine (e.g. "android_debug_unopt"). If the local engine build
-requires a source path, this can be provided by setting the `FLUTTER_LOCAL_ENGINE_SRC_PATH`
-environment variable. This second variable is not necessary if the `flutter` and
-`engine` checkouts are in adjacent directories.
+variant by setting the `FLUTTER_LOCAL_ENGINE` and `FLUTTER_LOCAL_ENGINE_HOST`
+environment svariable to the name of the local engines (e.g. `android_debug_unopt`
+and `host_debug_unopt`). If the local engine build requires a source path, this
+can be provided by setting the `FLUTTER_LOCAL_ENGINE_SRC_PATH` environment
+variable. This second variable is not necessary if the `flutter` and `engine`
+checkouts are in adjacent directories.
 
 ```shell
 export FLUTTER_LOCAL_ENGINE=android_debug_unopt
+export FLUTTER_LOCAL_ENGINE_HOST=host_debug_unopt
 flutter test test/integration.shard/some_test_case
 ```
 

packages/flutter_tools/test/integration.shard/test_utils.dart

@@ -67,6 +67,7 @@ Future<void> getPackages(String folder) async {
 }
 
 const String kLocalEngineEnvironment = 'FLUTTER_LOCAL_ENGINE';
+const String kLocalEngineHostEnvironment = 'FLUTTER_LOCAL_ENGINE_HOST';
 const String kLocalEngineLocation = 'FLUTTER_LOCAL_ENGINE_SRC_PATH';
 
 List<String> getLocalEngineArguments() {
@@ -75,6 +76,8 @@ List<String> getLocalEngineArguments() {
       '--local-engine=${platform.environment[kLocalEngineEnvironment]}',
     if (platform.environment.containsKey(kLocalEngineLocation))
       '--local-engine-src-path=${platform.environment[kLocalEngineLocation]}',
+    if (platform.environment.containsKey(kLocalEngineHostEnvironment))
+      '--local-engine-host=${platform.environment[kLocalEngineHostEnvironment]}',
   ];
 }