Kill compiler process when test does not exit cleanly (#34616)

packages/flutter_tools/lib/src/compile.dart

@@ -738,6 +738,7 @@ class ResidentCompiler {
     if (_server == null) {
       return 0;
     }
+    printTrace('killing pid ${_server.pid}');
     _server.kill();
     return _server.exitCode;
   }

packages/flutter_tools/lib/src/test/test_compiler.dart

@@ -85,6 +85,7 @@ class TestCompiler {
 
   Future<void> dispose() async {
     await compilerController.close();
+    await _shutdown();
   }
 
   /// Create the resident compiler used to compile the test.

packages/flutter_tools/test/test_compiler_test.dart

@@ -59,6 +59,15 @@ void main() {
 
       expect(await testCompiler.compile('test/foo.dart'), null);
       expect(fs.file('test/foo.dart.dill').existsSync(), false);
+      verify(residentCompiler.shutdown()).called(1);
+    }));
+
+    test('Disposing test compiler shuts down backing compiler', () => testbed.run(() async {
+      testCompiler.compiler = residentCompiler;
+      expect(testCompiler.compilerController.isClosed, false);
+      await testCompiler.dispose();
+      expect(testCompiler.compilerController.isClosed, true);
+      verify(residentCompiler.shutdown()).called(1);
     }));
   });
 }