Move pub over to using the pub.dartlang.org API v2.

sdk/lib/_internal/pub/test/descriptor/tar.dart

Index: sdk/lib/_internal/pub/test/descriptor/tar.dart
diff --git a/sdk/lib/_internal/pub/test/descriptor/tar.dart b/sdk/lib/_internal/pub/test/descriptor/tar.dart
index 02eca7c7e0e01a05b3309d84c5ada9483c3b8ae4..0dd8b826ce1a193ef86136e9e0f11724b1d6c11b 100644
--- a/sdk/lib/_internal/pub/test/descriptor/tar.dart
+++ b/sdk/lib/_internal/pub/test/descriptor/tar.dart
@@ -15,7 +15,8 @@ import '../../lib/src/io.dart';
 import '../../lib/src/utils.dart';
 
 /// Describes a tar file and its contents.
-class TarFileDescriptor extends DirectoryDescriptor {
+class TarFileDescriptor extends DirectoryDescriptor
+    implements ReadableDescriptor {
   TarFileDescriptor(String name, List<Descriptor> contents)
       : super(name, contents);