Add support for copying directory structures

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:convert';
 import 'dart:core';
@@ skipping 308 matching lines @@
   @override
   int get modificationStamp {
     int stamp = _provider._pathToTimestamp[path];
     if (stamp == null) {
       throw new FileSystemException(path, "File does not exist");
     }
     return stamp;
   }
 
   @override
+  File copyTo(Folder parentFolder) {
+    throw new FileSystemException(path, 'File could not be copied');
+  }
+
+  @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
@@ skipping 50 matching lines @@
   @override
   int get modificationStamp {
     int stamp = _provider._pathToTimestamp[path];
     if (stamp == null) {
       throw new FileSystemException(path, 'File "$path" does not exist.');
     }
     return stamp;
   }
 
   @override
+  File copyTo(Folder parentFolder) {
+    parentFolder.create();
+    File destination = parentFolder.getChildAssumingFile(shortName);
+    destination.writeAsBytesSync(readAsBytesSync());
+    return destination;
+  }
+
+  @override
   Source createSource([Uri uri]) {
     uri ??= _provider.pathContext.toUri(path);
     return new FileSource(this, uri);
   }
 
   @override
   void delete() {
     _provider.deleteFile(path);
   }
 
@@ skipping 56 matching lines @@
     childPath = _provider.pathContext.normalize(childPath);
     return childPath;
   }
 
   @override
   bool contains(String path) {
     return _provider.pathContext.isWithin(this.path, path);
   }
 
   @override
+  Folder copyTo(Folder parentFolder) {
+    Folder destination = parentFolder.getChildAssumingFolder(shortName);
+    destination.create();
+    for (Resource child in getChildren()) {
+      child.copyTo(destination);
+    }
+    return destination;
+  }
+
+  @override
+  void create() {
+    _provider.newFolder(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);
@@ skipping 95 matching lines @@
     }
     return path == other.path;
   }
 
   @override
   String toString() => path;
 
   @override
   Uri toUri() => _provider.pathContext.toUri(path);
 }