A couple of tweaks.

pkg/analyzer/lib/src/kernel/resynthesize.dart

Index: pkg/analyzer/lib/src/kernel/resynthesize.dart
diff --git a/pkg/analyzer/lib/src/kernel/resynthesize.dart b/pkg/analyzer/lib/src/kernel/resynthesize.dart
index cda1c2f8f22eee54b0bf72c75f89ba64f44d882f..3b21fbc5252436c7759638407267cfbec98a7dce 100644
--- a/pkg/analyzer/lib/src/kernel/resynthesize.dart
+++ b/pkg/analyzer/lib/src/kernel/resynthesize.dart
@@ -309,7 +309,7 @@ class _ExprBuilder {
       return AstTestFactory.typeName3(name)..type = type;
     }
     // TODO(scheglov) Implement for other types.
-    throw new UnimplementedError('type: $type');
+    throw new UnimplementedError('type: (${type.runtimeType}) $type');
   }
 
   TypeArgumentList _buildTypeArgumentList(List<kernel.DartType> kernels) {