Modify scanner and parser to be standalone packages.

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
new file mode 100644
index 0000000000000000000000000000000000000000..4b5faa7d8e23fabec7722a8dbefb6e3eca7247b9
--- /dev/null
+++ b/pkg/dart_scanner/lib/testing/scanner_chain.dart
@@ -0,0 +1,31 @@
+// Copyright (c) 2016, 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.md file.
+
+import 'package:testing/testing.dart';
+
+import 'package:scanner/scanner.dart';
+
+import 'package:scanner/io.dart';
+
+class Read extends Step<TestDescription, List<int>, ChainContext> {
+  const Read();
+
+  String get name => "read";
+
+  Future<Result<List<int>>> run(
+      TestDescription input, ChainContext context) async {
+    return pass(await readBytesFromFile(input.uri));
+  }
+}
+
+class Scan extends Step<List<int>, ScannerResult, ChainContext> {
+  const Scan();
+
+  String get name => "scan";
+
+  Future<Result<ScannerResult>> run(
+      List<int> bytes, ChainContext context) async {
+    return pass(scan(bytes));
+  }
+}