Add @overrides to (a lot of) analyzer.

pkg/analyzer/example/parser_driver.dart

 #!/usr/bin/env dart
 // Copyright (c) 2013, 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.
 
 import 'dart:io';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/src/dart/scanner/reader.dart';
@@ skipping 25 matching lines @@
 
   var visitor = new _ASTVisitor();
   unit.accept(visitor);
 
   for (var error in errorListener.errors) {
     print(error);
   }
 }
 
 class _ASTVisitor extends GeneralizingAstVisitor {
+  @override
   visitNode(AstNode node) {
     print('${node.runtimeType} : <"$node">');
     return super.visitNode(node);
   }
 }
 
 class _ErrorCollector extends AnalysisErrorListener {
   List<AnalysisError> errors;
   _ErrorCollector() : errors = new List<AnalysisError>();
+  @override
   onError(error) => errors.add(error);
 }