Make pkg/dart_messages strong.

pkg/dart_messages/bin/message_id.dart

Index: pkg/dart_messages/bin/message_id.dart
diff --git a/pkg/dart_messages/bin/message_id.dart b/pkg/dart_messages/bin/message_id.dart
index 7d59fbd18a1da98f0ec1feb6970a8a65c6c6f08c..a708e60a51f1bffee8461e9b6e862e57a7649600 100644
--- a/pkg/dart_messages/bin/message_id.dart
+++ b/pkg/dart_messages/bin/message_id.dart
@@ -4,7 +4,7 @@
 
 import 'dart:math' as math;
 
-import '../lib/shared_messages.dart' as shared_messages;
+import 'package:dart_messages/shared_messages.dart' as shared_messages;
 
 math.Random random = new math.Random();
 
@@ -13,7 +13,7 @@ final $A = "A".codeUnitAt(0);
 final $Z = "Z".codeUnitAt(0);
 
 String computeId() {
-  List charCodes = [];
+  List<int> charCodes = [];
   for (int i = 0; i < idLength; i++) {
     charCodes.add($A + random.nextInt($Z - $A));
   }