Add Resource.delete() method.

pkg/analyzer/lib/file_system/memory_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.memory_file_system;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:core' hide Resource;
 
@@ skipping 263 matching lines @@
   String get _content {
     throw new FileSystemException(path, 'File could not be read');
   }
 
   @override
   Source createSource([Uri uri]) {
     throw new FileSystemException(path, 'File could not be read');
   }
 
   @override
+  void delete() {
+    throw new FileSystemException(path, 'File could not be deleted');
+  }
+
+  @override
   bool isOrContains(String path) {
     return path == this.path;
   }
 
   @override
   List<int> readAsBytesSync() {
     throw new FileSystemException(path, 'File could not be read');
   }
 
   @override
@@ skipping 41 matching lines @@
 
   @override
   Source createSource([Uri uri]) {
     if (uri == null) {
       uri = _provider.pathContext.toUri(path);
     }
     return new _MemoryFileSource(this, uri);
   }
 
   @override
+  void delete() {
+    _provider.deleteFile(path);
+  }
+
+  @override
   bool isOrContains(String path) {
     return path == this.path;
   }
 
   @override
   List<int> readAsBytesSync() {
     List<int> bytes = _provider._pathToBytes[path];
     if (bytes == null) {
       throw new FileSystemException(path, 'File "$path" is not binary.');
     }
@@ skipping 126 matching lines @@
     childPath = _provider.pathContext.normalize(childPath);
     return childPath;
   }
 
   @override
   bool contains(String path) {
     return _provider.pathContext.isWithin(this.path, path);
   }
 
   @override
+  void delete() {
+    _provider.deleteFolder(path);
+  }
+
+  @override
   Resource getChild(String relPath) {
     String childPath = canonicalizePath(relPath);
     _MemoryResource resource = _provider._pathToResource[childPath];
     if (resource == null) {
       resource = new _MemoryFile(_provider, childPath);
     }
     return resource;
   }
 
   @override
@@ skipping 84 matching lines @@
   bool operator ==(other) {
     if (runtimeType != other.runtimeType) {
       return false;
     }
     return path == other.path;
   }
 
   @override
   String toString() => path;
 }