Use warning instead of error in a couple places. In polymer we are hitting

pkg/code_transformers/test/resolver_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library code_transformers.test.resolver_test;
 
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 import 'package:code_transformers/resolver.dart';
@@ skipping 152 matching lines @@
               main() {
               } ''',
           },
           validator: (resolver) {
             var lib = resolver.getLibrary(entryPoint);
             expect(lib.importedLibraries.length, 1);
           });
     });
 
     test('should fail on absolute URIs', () {
+      var warningPrefix = 'warning: absolute paths not allowed';
       return validateResolver(
           inputs: {
             'a|web/main.dart': '''
               import '/b.dart';
 
               main() {
               } ''',
           },
           messages: [
             // First from the AST walker
-            'error: absolute paths not allowed: "/b.dart" (web/main.dart 0 14)',
-            'error: absolute paths not allowed: "/b.dart"',
+            '$warningPrefix: "/b.dart" (web/main.dart 0 14)',
+            '$warningPrefix: "/b.dart"',
           ],
           validator: (resolver) {
             var lib = resolver.getLibrary(entryPoint);
             expect(lib.importedLibraries.length, 1);
           });
     });
 
     test('should list all libraries', () {
       return validateResolver(
           inputs: {
@@ skipping 156 matching lines @@
 
   TestTransformer(Resolvers resolvers, this.primary, this.validator) {
     this.resolvers = resolvers;
   }
 
   Future<bool> isPrimary(Asset input) =>
       new Future.value(input.id == primary);
 
   applyResolver(Transform transform, Resolver resolver) => validator(resolver);
 }