Implement AstBuilder support for `void` keyword.

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:front_end/src/fasta/scanner/token.dart'
     show BeginGroupToken, Token;
 
 import 'package:analyzer/analyzer.dart';
@@ skipping 1048 matching lines @@
         toAnalyzerToken(separator),
         initializers,
         redirectedConstructor,
         body));
   }
 
   @override
   void endMember() {
     debugEvent("Member");
   }
+
+  @override
+  void handleVoidKeyword(Token token) {
+    debugEvent("VoidKeyword");
+    // TODO(paulberry): is this sufficient, or do we need to hook the "void"
+    // keyword up to an element?
+    handleIdentifier(token);
+    handleNoTypeArguments(token);
+    endType(token, token);
+  }
 }
 
 /// Data structure placed on the stack to represent a class body.
 ///
 /// This is needed because analyzer has no separate AST representation of a
 /// class body; it simply stores all of the relevant data in the
 /// [ClassDeclaration] object.
 class _ClassBody {
   final Token beginToken;
 
@@ skipping 12 matching lines @@
 /// [ClassDeclaration] or [ClassTypeAlias] object.
 class _MixinApplication {
   final TypeName supertype;
 
   final Token withKeyword;
 
   final List<TypeName> mixinTypes;
 
   _MixinApplication(this.supertype, this.withKeyword, this.mixinTypes);
 }