Add @overrides to (a lot of) analyzer.

pkg/analyzer/example/resolver_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/dart/element/element.dart';
@@ skipping 39 matching lines @@
   CompilationUnit resolvedUnit =
       context.resolveCompilationUnit(source, libElement);
   var visitor = new _ASTVisitor();
   resolvedUnit.accept(visitor);
 }
 
 const _usage =
     'Usage: resolve_driver <path_to_sdk> <file_to_resolve> [<packages_root>]';
 
 class _ASTVisitor extends GeneralizingAstVisitor {
+  @override
   visitNode(AstNode node) {
     var lines = <String>['${node.runtimeType} : <"$node">'];
     if (node is SimpleIdentifier) {
       Element element = node.staticElement;
       if (element != null) {
         lines.add('  element: ${element.runtimeType}');
         LibraryElement library = element.library;
         if (library != null) {
           var fullName =
               element.library.definingCompilationUnit.source.fullName;
           lines.add("  from $fullName");
         }
       }
     }
     print(lines.join('\n'));
     return super.visitNode(node);
   }
 }