Implementation of async-await transformation on js ast.

pkg/compiler/lib/src/apiimpl.dart

 // Copyright (c) 2012, 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 leg_apiimpl;
 
 import 'dart:async';
 
 import '../compiler.dart' as api;
 import 'dart2jslib.dart' as leg;
@@ skipping 66 matching lines @@
                 "build number could not be determined"),
             showPackageWarnings:
                 hasOption(options, '--show-package-warnings'),
             useContentSecurityPolicy: hasOption(options, '--csp'),
             hasIncrementalSupport:
                 forceIncrementalSupport ||
                 hasOption(options, '--incremental-support'),
             suppressWarnings: hasOption(options, '--suppress-warnings'),
             enableExperimentalMirrors:
                 hasOption(options, '--enable-experimental-mirrors'),
-            enableAsyncAwait: hasOption(options, '--enable-async'),
             generateCodeWithCompileTimeErrors:
                 hasOption(options, '--generate-code-with-compile-time-errors'),
             allowNativeExtensions:
                 hasOption(options, '--allow-native-extensions')) {
     tasks.addAll([
         userHandlerTask = new leg.GenericTask('Diagnostic handler', this),
         userProviderTask = new leg.GenericTask('Input provider', this),
     ]);
     if (libraryRoot == null) {
       throw new ArgumentError("[libraryRoot] is null.");
     }
     if (!libraryRoot.path.endsWith("/")) {
       throw new ArgumentError("[libraryRoot] must end with a /.");
     }
     if (packageRoot == null) {
       throw new ArgumentError("[packageRoot] is null.");
     }
     if (!packageRoot.path.endsWith("/")) {
       throw new ArgumentError("[packageRoot] must end with a /.");
     }
     if (!analyzeOnly) {
-      if (enableAsyncAwait && emitJavaScript) {
-        throw new ArgumentError(
-            "--enable-async is currently only supported with --analyze-only");
-      }
       if (allowNativeExtensions) {
         throw new ArgumentError(
             "--allow-native-extensions is only supported in combination with "
             "--analyze-only");
       }
     }
   }
 
   static String extractStringOption(List<String> options,
                                     String prefix,
@@ skipping 282 matching lines @@
     print('$message: ${tryToString(exception)}');
     print(tryToString(stackTrace));
   }
 
   fromEnvironment(String name) => environment[name];
 
   LibraryInfo lookupLibraryInfo(String libraryName) {
     return library_info.LIBRARIES[libraryName];
   }
 }