Apply several phases only to entrypoint files (which currently are identified as

pkg/polymer/lib/src/transform/import_inliner.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 inlines polymer-element definitions from html imports. */
 library polymer.src.transform.import_inliner;
 
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 import 'package:path/path.dart' as path;
 import 'package:html5lib/dom.dart' show Document, Node, DocumentFragment;
 import 'package:html5lib/dom_parsing.dart' show TreeVisitor;
 import 'common.dart';
 
 /** Recursively inlines polymer-element definitions from html imports. */
 // TODO(sigmund): make sure we match semantics of html-imports for tags other
 // than polymer-element (see dartbug.com/12613).
 class ImportedElementInliner extends Transformer {
-  /** Only run this transformer on .html files. */
-  final String allowedExtensions = ".html";
+  /** Only run on entry point .html files. */
+  Future<bool> isPrimary(Asset input) => isPrimaryHtml(input.id);
 
   Future apply(Transform transform) {
     var seen = new Set<AssetId>();
     var elements = [];
     var id = transform.primaryInput.id;
     seen.add(id);
     return transform.primaryInput.readAsString().then((content) {
       var document = parseHtml(content, id.path, transform.logger);
       var future = _visitImports(document, id, transform, seen, elements);
       return future.then((importsFound) {
@@ skipping 44 matching lines @@
     }).then((_) => true);
   }
 
   /**
    * Loads an asset identified by [id], visits its imports and collects it's
    * polymer-element definitions.
    */
   Future _collectPolymerElements(AssetId id, Transform transform,
       Set<AssetId> seen, List elements) {
     return transform.readInputAsString(id).then((content) {
-      var document = parseHtml(
-          content, id.path, transform.logger, checkDocType: false);
+      var document = parseHtml(content, id.path, transform.logger,
+          checkDocType: false);
       return _visitImports(document, id, transform, seen, elements).then((_) {
         var normalizer = new _UrlNormalizer(transform, id);
         for (var element in document.queryAll('polymer-element')) {
           normalizer.visit(document);
           elements.add(element);
         }
       });
     });
   }
 }
@@ skipping 63 matching lines @@
   'cite',       // in blockquote, del, ins, q
   'data',       // in object
   'formaction', // in button, input
   'href',       // in a, area, link, base, command
   'icon',       // in command
   'manifest',   // in html
   'poster',     // in video
   'src',        // in audio, embed, iframe, img, input, script, source, track,
                 //    video
 ];