Add support for copying directory structures

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';
 import 'dart:io' as io;
 
@@ skipping 132 matching lines @@
       throw new FileSystemException(exception.path, exception.message);
     }
   }
 
   /**
    * Return the underlying file being represented by this wrapper.
    */
   io.File get _file => _entry as io.File;
 
   @override
+  File copyTo(Folder parentFolder) {
+    parentFolder.create();
+    File destination = parentFolder.getChildAssumingFile(shortName);
+    destination.writeAsBytesSync(readAsBytesSync());
+    return destination;
+  }
+
+  @override
   Source createSource([Uri uri]) {
     return new FileSource(this, uri ?? pathContext.toUri(path));
   }
 
   @override
   bool isOrContains(String path) {
     return path == this.path;
   }
 
   @override
@@ skipping 76 matching lines @@
   String canonicalizePath(String relPath) {
     return normalize(join(path, relPath));
   }
 
   @override
   bool contains(String path) {
     return absolutePathContext.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() {
+    _directory.createSync(recursive: true);
+  }
+
+  @override
   Resource getChild(String relPath) {
     String canonicalPath = canonicalizePath(relPath);
     return PhysicalResourceProvider.INSTANCE.getResource(canonicalPath);
   }
 
   @override
   _PhysicalFile getChildAssumingFile(String relPath) {
     String canonicalPath = canonicalizePath(relPath);
     io.File file = new io.File(canonicalPath);
     return new _PhysicalFile(file);
@@ skipping 156 matching lines @@
           timer.cancel();
         }
       });
       return completer.future;
     }
     _isSpawning = true;
     _runner = await IsolateRunner.spawn();
     return _runner;
   }
 }