Add support for parsing #void with Fasta.

pkg/front_end/lib/src/fasta/analyzer/ast_builder.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.analyzer.ast_builder;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/ast/ast_factory.dart' show AstFactory;
 import 'package:analyzer/dart/ast/standard_ast_factory.dart' as standard;
 import 'package:analyzer/dart/ast/token.dart' as analyzer show Token;
@@ skipping 257 matching lines @@
     pop(); // Token.
     receiver.cascadeSections.add(expression);
     push(receiver);
   }
 
   void handleOperator(Token token) {
     debugEvent("Operator");
     push(toAnalyzerToken(token));
   }
 
+  void handleSymbolVoid(Token token) {
+    debugEvent("SymbolVoid");
+    push(toAnalyzerToken(token));
+  }
+
   void handleBinaryExpression(Token token) {
     debugEvent("BinaryExpression");
     if (identical(".", token.stringValue) ||
         identical("?.", token.stringValue) ||
         identical("..", token.stringValue)) {
       doDotExpression(token);
     } else {
       Expression right = pop();
       Expression left = pop();
       push(ast.binaryExpression(left, toAnalyzerToken(token), right));
@@ skipping 1168 matching lines @@
       } else if (identical('static', s)) {
         staticKeyword = token;
       } else if (identical('var', s)) {
         finalConstOrVarKeyword = token;
       } else {
         internalError('Unhandled modifier: $s');
       }
     }
   }
 }