Step one towards stable error messages with details:

pkg/polymer/test/build/common.dart

Index: pkg/polymer/test/build/common.dart
diff --git a/pkg/polymer/test/build/common.dart b/pkg/polymer/test/build/common.dart
index b6da27a82df310487e128216aec635825cc646e9..13411e66eda9801c2895eba5e736b1eb733f0437 100644
--- a/pkg/polymer/test/build/common.dart
+++ b/pkg/polymer/test/build/common.dart
@@ -7,6 +7,8 @@ library polymer.test.build.common;
 import 'dart:async';
 
 import 'package:barback/barback.dart';
+import 'package:code_transformers/messages/build_logger.dart'
+  show LOG_EXTENSION;
 import 'package:polymer/src/build/common.dart';
 import 'package:stack_trace/stack_trace.dart';
 import 'package:unittest/unittest.dart';