add enableAsync to analysis option file flags

pkg/analysis_server/test/integration/analysis/error_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library test.integration.analysis.error;
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../utils.dart';
 import '../integration_tests.dart';
 
 main() {
   initializeTestEnvironment();
   defineReflectiveTests(AnalysisErrorIntegrationTest);
 }
 
 @reflectiveTest
 class AnalysisErrorIntegrationTest
     extends AbstractAnalysisServerIntegrationTest {
+  test_async_disabled() async {
+    String pathname = sourcePath('test.dart');
+    writeFile(
+        pathname,
+        '''
+import 'dart:async';
+class Test {
+  Future foo() async {}
+}
+  ''');
+    await sendAnalysisUpdateOptions(new AnalysisOptions()..enableAsync = false);
+    standardAnalysisSetup();
+    await analysisFinished;
+    expect(currentAnalysisErrors[pathname], isList);
+    List<AnalysisError> errors = currentAnalysisErrors[pathname];
+    expect(errors, hasLength(1));
+    Set<String> allErrorMessages =
+        errors.map((AnalysisError e) => e.message).toSet();
+    expect(allErrorMessages, contains(
+      "Async and sync are not supported in this environment."));
+  }
+
+  test_async_enabled() async {
+    String pathname = sourcePath('test.dart');
+    writeFile(
+        pathname,
+        '''
+import 'dart:async';
+class Test {
+  Future foo() async {}
+}
+  ''');
+    standardAnalysisSetup();
+    await analysisFinished;
+    expect(currentAnalysisErrors[pathname], isList);
+    List<AnalysisError> errors = currentAnalysisErrors[pathname];
+    expect(errors, isEmpty);
+  }
+
   test_detect_simple_error() {
     String pathname = sourcePath('test.dart');
     writeFile(
         pathname,
         '''
 main() {
   print(null) // parse error: missing ';'
 }''');
     standardAnalysisSetup();
     return analysisFinished.then((_) {
@@ skipping 57 matching lines @@
 ''');
     await sendAnalysisUpdateOptions(
         new AnalysisOptions()..enableSuperMixins = true);
     standardAnalysisSetup();
     await analysisFinished;
     expect(currentAnalysisErrors[pathname], isList);
     List<AnalysisError> errors = currentAnalysisErrors[pathname];
     expect(errors, isEmpty);
   }
 }