Add Resource.delete() method.

pkg/analyzer/lib/file_system/physical_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.physical_file_system;
 
 import 'dart:async';
 import 'dart:core' hide Resource;
 import 'dart:io' as io;
 
@@ skipping 245 matching lines @@
 
   @override
   bool operator ==(other) {
     if (runtimeType != other.runtimeType) {
       return false;
     }
     return path == other.path;
   }
 
   @override
+  void delete() {
+    try {
+      _entry.deleteSync(recursive: true);
+    } on io.FileSystemException catch (exception) {
+      throw new FileSystemException(exception.path, exception.message);
+    }
+  }
+
+  @override
   String toString() => path;
 }