add tool to check that deferred libraries contain the expected code

lib/json_info_codec.dart

Index: lib/json_info_codec.dart
diff --git a/lib/json_info_codec.dart b/lib/json_info_codec.dart
index 1293d305cf548266f9314e85592ad7662cd7cc3e..6ee76346853f186b4a9d9590ccbc3830dd7047eb 100644
--- a/lib/json_info_codec.dart
+++ b/lib/json_info_codec.dart
@@ -48,11 +48,21 @@ class JsonToAllInfoConverter extends Converter<Map, AllInfo> {
       result.dependencies[idMap[k]] = deps.map((d) => idMap[d]).toList();
     });
 
+    result.outputUnits.addAll(json['outputUnits'].map(parseOutputUnit));
+
     result.program = parseProgram(json['program']);
     // todo: version, etc
     return result;
   }
 
+  OutputUnitInfo parseOutputUnit(Map json) {
+    OutputUnitInfo result = parseId(json['id']);
+    result
+      ..name = json['name']
+      ..size = json['size'];
+    return result;
+  }
+
   LibraryInfo parseLibrary(Map json) {
     LibraryInfo result = parseId(json['id']);
     result