Fix parsing [a]sync[*] function body modifiers with Fasta.

pkg/front_end/lib/src/fasta/source/diet_listener.dart

 // Copyright (c) 2016, 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 fasta.diet_listener;
 
 import 'package:kernel/ast.dart' show AsyncMarker;
 
 import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;
 
@@ skipping 477 matching lines @@
 
   void parseFunctionBody(StackListener listener, Token token) {
     try {
       Parser parser = new Parser(listener);
       token = parser.parseFormalParametersOpt(token);
       var formals = listener.pop();
       listener.checkEmpty(token.charOffset);
       listener.prepareInitializers();
       token = parser.parseInitializersOpt(token);
       token = parser.parseAsyncModifier(token);
-      AsyncMarker asyncModifier = listener.pop();
+      AsyncMarker asyncModifier =
+          astKind == AstKind.Analyzer ? null : listener.pop();
       bool isExpression = false;
       bool allowAbstract = true;
       parser.parseFunctionBody(token, isExpression, allowAbstract);
       var body = listener.pop();
       listener.checkEmpty(token.charOffset);
       listener.finishFunction(formals, asyncModifier, body);
     } on InputError {
       rethrow;
     } catch (e, s) {
       throw new Crash(uri, token.charOffset, e, s);
@@ skipping 49 matching lines @@
   bool get isTargetingDartVm {
     // TODO(ahe): Find a more reliable way to check if this is the Dart VM.
     return !coreTypes.containsLibrary("dart:_js_helper");
   }
 
   @override
   void debugEvent(String name) {
     // printEvent(name);
   }
 }