Add @overrides to (a lot of) analyzer.

pkg/analyzer/lib/file_system/file_system.dart

 // Copyright (c) 2014, 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 analyzer.file_system.file_system;
 
 import 'dart:async';
 
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/util/absolute_path.dart';
@@ skipping 29 matching lines @@
 
 /**
  * Base class for all file system exceptions.
  */
 class FileSystemException implements Exception {
   final String path;
   final String message;
 
   FileSystemException(this.path, this.message);
 
+  @override
   String toString() => 'FileSystemException(path=$path; message=$message)';
 }
 
 /**
  * [Folder]s are [Resource]s which may contain files and/or other folders.
  */
 abstract class Folder implements Resource {
   /**
    * Watch for changes to the files inside this folder (and in any nested
    * folders, including folders reachable via links).
@@ skipping 141 matching lines @@
 
   @override
   Uri restoreAbsolute(Source source) =>
       _provider.pathContext.toUri(source.fullName);
 
   /**
    * Return `true` if the given [uri] is a `file` URI.
    */
   static bool _isFileUri(Uri uri) => uri.scheme == _FILE_SCHEME;
 }