Add support for copying directory structures

pkg/analyzer/lib/file_system/memory_file_system.dart

Index: pkg/analyzer/lib/file_system/memory_file_system.dart
diff --git a/pkg/analyzer/lib/file_system/memory_file_system.dart b/pkg/analyzer/lib/file_system/memory_file_system.dart
index 3cab6ee8995aed9cfaed5d5a10d6a66cc98174a8..6e7ab642e104bd94fd18f642df1b0a51759f54a6 100644
--- a/pkg/analyzer/lib/file_system/memory_file_system.dart
+++ b/pkg/analyzer/lib/file_system/memory_file_system.dart
@@ -326,6 +326,11 @@ class _MemoryDummyLink extends _MemoryResource implements File {
   }
 
   @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');
   }
@@ -396,6 +401,14 @@ class _MemoryFile extends _MemoryResource implements File {
   }
 
   @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);
@@ -472,6 +485,21 @@ class _MemoryFolder extends _MemoryResource implements Folder {
   }
 
   @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);
   }