Only pass an AssetId to isPrimary and declareOutputs.

pkg/polymer/lib/src/build/build_filter.dart

 // Copyright (c) 2013, 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.
 
 /// Final phase of the polymer transformation: removes any files that are not
 /// needed for deployment.
 library polymer.src.build.build_filter;
 
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 import 'common.dart';
 
 /// Removes any files not needed for deployment, such as internal build
 /// artifacts and non-entry HTML files.
 class BuildFilter extends Transformer with PolymerTransformer {
   final TransformOptions options;
   BuildFilter(this.options);
 
-  Future<bool> isPrimary(Asset input) => new Future.value(
+  // TODO(nweiz): This should just take an AssetId when barback <0.13.0 support
+  // is dropped.
+  Future<bool> isPrimary(idOrAsset) {
+    var id = idOrAsset is AssetId ? idOrAsset : idOrAsset.id;
+    return new Future.value(
       // nothing is filtered in debug mode
       options.releaseMode &&
       // TODO(sigmund): remove this exclusion once we have dev_transformers
       // (dartbug.com/14187)
-      input.id.path.startsWith('web/') &&
+      id.path.startsWith('web/') &&
       // may filter non-entry HTML files and internal artifacts
-      (input.id.extension == '.html' || input.id.extension == '.scriptUrls') &&
+      (id.extension == '.html' || id.extension == '.scriptUrls') &&
       // keep any entry points
-      !options.isHtmlEntryPoint(input.id));
+      !options.isHtmlEntryPoint(id));
+  }
 
   Future apply(Transform transform) {
     if (transform.primaryInput.id.extension == '.scriptUrls') {
       return new Future.value(null);
     }
     return readPrimaryAsHtml(transform).then((document) {
       // Keep .html files that don't use polymer, since the app developer might
       // have non-polymer entrypoints.
       if (document.querySelectorAll('polymer-element').isEmpty) {
         transform.addOutput(transform.primaryInput);
       }
     });
   }
 }