add a JsonInfoCodec class

bin/verify_deps.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.
 
 /// This tools verifies that all elements that are included in the output are
 /// reachable from the program entrypoint. If there are elements that are not
 /// reachable from the entrypoint, then this indicates that we are missing
 /// dependencies. If all functions are reachable from the entrypoint, this
 /// script will return with exitcode 0. Otherwise it will list the unreachable
 /// functions and return with exitcode 1.
 library dart2js_info.bin.verify_deps;
 
 import 'dart:async';
 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';
 
 Future main(List<String> args) async {
   if (args.length > 1) {
     printUsage();
     exit(1);
   }
   var json = JSON.decode(await new File(args[0]).readAsString());
-  var info = new AllInfo.fromJson(json);
+  var info = new AllInfoJsonCodec().decode(json);
   var graph = graphFromInfo(info);
   var entrypoint = info.program.entrypoint;
   var reachables = findReachable(graph, entrypoint);
 
   var unreachables = info.functions.where((func) => !reachables.contains(func));
   if (unreachables.isNotEmpty) {
     unreachables.forEach(print);
     exit(1);
   } else {
     print('all elements are reachable from the entrypoint');
   }
 }
 
 /// Finds the set of nodes reachable from [start] in [graph].
 Set<Info> findReachable(Graph<Info> graph, Info start) {
   var visited = new Set<Info>();
   var stack = <Info>[start];
   while (stack.isNotEmpty) {
     var next = stack.removeLast();
     visited.add(next);
     stack.addAll(
         graph.targetsOf(next).where((target) => !visited.contains(target)));
   }
   return visited;
 }
 
 void printUsage() {
   print('usage: dart2js_info_verify_deps <info file>');
 }