add tool to get breakdown of deferred libraries by size

bin/debug_info.dart

 // Copyright (c) 2015, 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 file.
 
 /// Tool used mainly by dart2js developers to debug the generated info and check
 /// that it is consistent and that it covers all the data we expect it to cover.
 library dart2js_info.bin.debug_info;
 
-import 'dart:convert';
 import 'dart:io';
 
 import 'package:dart2js_info/info.dart';
 import 'package:dart2js_info/src/graph.dart';
 import 'package:dart2js_info/src/util.dart';
 
-main(args) {
+main(args) async {
   if (args.length < 1) {
     print('usage: dart tool/debug_info.dart path-to-info.json '
         '[--show-library libname]');
     exit(1);
   }
 
-  var filename = args[0];
-  var json = JSON.decode(new File(filename).readAsStringSync());
-  var info = new AllInfoJsonCodec().decode(json);
+  var info = await infoFromFile(args.first);
   var debugLibName;
 
   if (args.length > 2 && args[1] == '--show-library') {
     debugLibName = args[2];
   }
 
   validateSize(info, debugLibName);
   compareGraphs(info);
   verifyDeps(info);
 }
@@ skipping 241 matching lines @@
   if (unreachables.isNotEmpty) {
     _fail('${unreachables.length} elements are unreachable from the '
         'entrypoint');
   } else {
     _pass('all elements are reachable from the entrypoint');
   }
 }
 
 _pass(String msg) => print('\x1b[32mPASS\x1b[0m: $msg');
 _fail(String msg) => print('\x1b[31mFAIL\x1b[0m: $msg');