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

pkg/code_transformers/test/assets_test.dart

Index: pkg/code_transformers/test/assets_test.dart
diff --git a/pkg/code_transformers/test/assets_test.dart b/pkg/code_transformers/test/assets_test.dart
index 7030e48d3c5635c2427294cf9dc7e0a6908345f7..4d394305ca43279af54df4aae08489f93b8aac4b 100644
--- a/pkg/code_transformers/test/assets_test.dart
+++ b/pkg/code_transformers/test/assets_test.dart
@@ -66,7 +66,7 @@ main() {
     testAssetUri('does not allow packages from non-dart lib files',
         source: new AssetId('a', 'lib/index.html'),
         uri: 'packages/foo/bar',
-        message: 'error: Invalid url to reach to another package: '
+        message: 'warning: Invalid url to reach to another package: '
             'packages/foo/bar. Path reaching to other packages must first '
             'reach up all the way to the packages folder. For example, try '
             'changing the url above to: ../../packages/foo/bar');
@@ -79,12 +79,13 @@ main() {
     testAssetUri('does not allow package: imports from non-dart files',
         source: new AssetId('a', 'lib/index.html'),
         uri: 'package:foo/bar.dart',
-        message: 'error: absolute paths not allowed: "package:foo/bar.dart"');
+        message: 'warning: absolute paths not allowed: "package:foo/bar.dart"');
 
     testAssetUri('does not allow absolute /packages by default',
         source: new AssetId('a', 'lib/index.html'),
         uri: '/packages/foo/bar.dart',
-        message: 'error: absolute paths not allowed: "/packages/foo/bar.dart"');
+        message:
+            'warning: absolute paths not allowed: "/packages/foo/bar.dart"');
 
     testAssetUri('can suppress error on absolute /packages ',
         source: new AssetId('a', 'lib/index.html'),