add a JsonInfoCodec class

bin/live_code_size_analysis.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.
 
 /// Command-line tool presenting combined information from dump-info and
 /// coverage data.
 ///
 /// This tool requires two input files an `.info.json` and a
 /// `.coverage.json` file. To produce these files you need to follow these
 /// steps:
@@ skipping 31 matching lines @@
 import 'function_size_analysis.dart';
 
 main(args) {
   if (args.length < 2) {
     print('usage: dart tool/live_code_size_analysis.dart path-to-info.json '
         'path-to-coverage.json [-v]');
     exit(1);
   }
 
   var json = JSON.decode(new File(args[0]).readAsStringSync());
-  var info = new AllInfo.fromJson(json);
+  var info = new AllInfoJsonCodec().decode(json);
   var coverage = JSON.decode(new File(args[1]).readAsStringSync());
   var verbose = args.length > 2 && args[2] == '-v';
 
   int realTotal = info.program.size;
   int totalLib = info.libraries.fold(0, (n, lib) => n + lib.size);
 
   int totalCode = 0;
   int reachableCode = 0;
   List<Info> unused = [];
 
@@ skipping 47 matching lines @@
 }
 
 _showHeader(String msg, String header1, String header2) {
   print(' ${pad(msg, 30, right: true)} ${pad(header1, 8)} ${pad(header2, 6)}');
 }
 
 _show(String msg, int size, int total) {
   var percent = (size * 100 / total).toStringAsFixed(2);
   print(' ${pad(msg, 30, right: true)} ${pad(size, 8)} ${pad(percent, 6)}%');
 }