Move all main methods to tool/.

pkg/front_end/lib/src/fasta/testing/scanner_chain.dart

Index: pkg/front_end/lib/src/fasta/testing/scanner_chain.dart
diff --git a/pkg/front_end/lib/src/fasta/scanner/testing/scanner_chain.dart b/pkg/front_end/lib/src/fasta/testing/scanner_chain.dart
similarity index 88%
rename from pkg/front_end/lib/src/fasta/scanner/testing/scanner_chain.dart
rename to pkg/front_end/lib/src/fasta/testing/scanner_chain.dart
index 05020c780aae1e4729e518b1ad69aa930fec4ef6..277697e297ed477afe061a9441f7afeb145e1cd1 100644
--- a/pkg/front_end/lib/src/fasta/scanner/testing/scanner_chain.dart
+++ b/pkg/front_end/lib/src/fasta/testing/scanner_chain.dart
@@ -2,13 +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 fasta.scanner.testing.scanner_chain;
+library fasta.testing.scanner_chain;
 
 import 'package:testing/testing.dart';
 
-import '../../scanner.dart';
+import '../scanner.dart';
 
-import '../io.dart';
+import '../scanner/io.dart';
 
 class Read extends Step<TestDescription, List<int>, ChainContext> {
   const Read();