Move all main methods to tool/.

pkg/front_end/test/fasta/parser/parser_suite.dart

 // 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:front_end/src/fasta/scanner.dart';
 
-import 'package:front_end/src/fasta/scanner/testing/scanner_chain.dart';
+import 'package:front_end/src/fasta/testing/scanner_chain.dart';
 
 import 'package:front_end/src/fasta/parser.dart';
 
 Future<ChainContext> createContext(
     Chain suite, Map<String, String> enviroment) async {
   return new ScannerContext();
 }
 
 class ScannerContext extends ChainContext {
   final List<Step> steps = const <Step>[
@@ skipping 16 matching lines @@
         return fail(null, errors.join("\n"));
       }
     } on ParserError catch (e, s) {
       return fail(null, e, s);
     }
     return pass(null);
   }
 }
 
 main(List<String> arguments) => runMe(arguments, createContext);