Add support for copying directory structures

pkg/analyzer/lib/file_system/physical_file_system.dart

Index: pkg/analyzer/lib/file_system/physical_file_system.dart
diff --git a/pkg/analyzer/lib/file_system/physical_file_system.dart b/pkg/analyzer/lib/file_system/physical_file_system.dart
index b190c1bf9a45cd6946163b89c2f89df94d814597..f3906be89b2ffff8c81dc929504dfe1bd9cfc848 100644
--- a/pkg/analyzer/lib/file_system/physical_file_system.dart
+++ b/pkg/analyzer/lib/file_system/physical_file_system.dart
@@ -150,6 +150,14 @@ class _PhysicalFile extends _PhysicalResource implements File {
   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));
   }
@@ -246,6 +254,21 @@ class _PhysicalFolder extends _PhysicalResource 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() {
+    _directory.createSync(recursive: true);
+  }
+
+  @override
   Resource getChild(String relPath) {
     String canonicalPath = canonicalizePath(relPath);
     return PhysicalResourceProvider.INSTANCE.getResource(canonicalPath);