add tool to get breakdown of deferred libraries by size

bin/function_size_analysis.dart

Index: bin/function_size_analysis.dart
diff --git a/bin/function_size_analysis.dart b/bin/function_size_analysis.dart
index 3606310c1102e09708e72ee8dc75c07ff1e89053..e97166da114268a6af6f0256910848fc15bd5700 100644
--- a/bin/function_size_analysis.dart
+++ b/bin/function_size_analysis.dart
@@ -6,17 +6,14 @@
 /// code.
 library compiler.tool.live_code_size_analysis;
 
-import 'dart:convert';
-import 'dart:io';
 import 'dart:math' as math;
 
 import 'package:dart2js_info/info.dart';
 import 'package:dart2js_info/src/graph.dart';
 import 'package:dart2js_info/src/util.dart';
 
-main(args) {
-  var json = JSON.decode(new File(args[0]).readAsStringSync());
-  var info = new AllInfoJsonCodec().decode(json);
+main(args) async {
+  var info = await infoFromFile(args.first);
   showCodeDistribution(info);
 }