Update scanner so tests pass.

pkg/dart_scanner/lib/testing/scanner_chain.dart

Index: pkg/dart_scanner/lib/testing/scanner_chain.dart
diff --git a/pkg/dart_scanner/lib/testing/scanner_chain.dart b/pkg/dart_scanner/lib/testing/scanner_chain.dart
index 4b5faa7d8e23fabec7722a8dbefb6e3eca7247b9..55898f12369147ae01b77439170b1616045e3d74 100644
--- a/pkg/dart_scanner/lib/testing/scanner_chain.dart
+++ b/pkg/dart_scanner/lib/testing/scanner_chain.dart
@@ -2,11 +2,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+library dart_scanner.testing.scanner_chain;
+
 import 'package:testing/testing.dart';
 
-import 'package:scanner/scanner.dart';
+import 'package:dart_scanner/scanner.dart';
 
-import 'package:scanner/io.dart';
+import 'package:dart_scanner/io.dart';
 
 class Read extends Step<TestDescription, List<int>, ChainContext> {
   const Read();