Only pass an AssetId to isPrimary and declareOutputs.

pkg/polymer/lib/src/build/script_compactor.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.
 
 /// Transfomer that combines multiple dart script tags into a single one.
 library polymer.src.build.script_compactor;
 
 import 'dart:async';
 import 'dart:convert';
 
@@ skipping 31 matching lines @@
 /// statement to a library, and then uses `initPolymer` (see polymer.dart)  to
 /// process `@initMethod` and `@CustomTag` annotations in those libraries.
 class ScriptCompactor extends Transformer {
   final Resolvers resolvers;
   final TransformOptions options;
 
   ScriptCompactor(this.options, {String sdkDir})
       : resolvers = new Resolvers(sdkDir != null ? sdkDir : dartSdkDirectory);
 
   /// Only run on entry point .html files.
-  Future<bool> isPrimary(Asset input) =>
-      new Future.value(options.isHtmlEntryPoint(input.id));
+  // 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(options.isHtmlEntryPoint(id));
+  }
 
   Future apply(Transform transform) =>
       new _ScriptCompactor(transform, options, resolvers).apply();
 }
 
 /// Helper class mainly use to flatten the async code.
 class _ScriptCompactor extends PolymerTransformer {
   final TransformOptions options;
   final Transform transform;
   final TransformLogger logger;
@@ skipping 620 matching lines @@
   for (var c in combinators) {
     if (c is ShowElementCombinator) {
       var show = c.shownNames.toSet();
       elements.retainWhere((e) => show.contains(e.displayName));
     } else if (c is HideElementCombinator) {
       var hide = c.hiddenNames.toSet();
       elements.removeWhere((e) => hide.contains(e.displayName));
     }
   }
 }