normalize url attributes on entry point elements

pkg/polymer/lib/src/build/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.build.import_inliner;
 
 import 'dart:async';
 import 'dart:convert';
 
@@ skipping 27 matching lines @@
 
   _HtmlInliner(this.options, Transform transform)
       : transform = transform,
         logger = transform.logger,
         docId = transform.primaryInput.id;
 
   Future apply() {
     seen.add(docId);
 
     Document document;
-    bool changed;
+    bool changed = false;
 
     return readPrimaryAsHtml(transform).then((doc) {
       document = doc;
+      changed = new _UrlNormalizer(transform, docId).visit(document) || changed;
+      
       experimentalBootstrap = document.querySelectorAll('link').any((link) =>
           link.attributes['rel'] == 'import' &&
           link.attributes['href'] == POLYMER_EXPERIMENTAL_HTML);
-      changed = _extractScripts(document);
+      changed = _extractScripts(document) || changed;
       return _visitImports(document);
     }).then((importsFound) {
       changed = changed || importsFound;
       return _removeScripts(document);
     }).then((scriptsRemoved) {
       changed = changed || scriptsRemoved;
 
       var output = transform.primaryInput;
       if (changed) output = new Asset.fromString(docId, document.outerHtml);
       transform.addOutput(output);
@@ skipping 229 matching lines @@
   /// Asset where the original content (and original url) was found.
   final AssetId sourceId;
 
   /// Counter used to ensure that every library name we inject is unique.
   int _count = 0;
 
   /// Path to the top level folder relative to the transform primaryInput.
   /// This should just be some arbitrary # of ../'s.
   final String topLevelPath;
 
+  /// Whether or not the normalizer has changed something in the tree.
+  bool changed = false;
+
   _UrlNormalizer(transform, this.sourceId)
       : transform = transform,
         topLevelPath =
           '../' * (transform.primaryInput.id.path.split('/').length - 2);
 
+  visit(Element node) {
+    super.visit(node);
+    return changed;
+  }
+
   visitElement(Element node) {
     // TODO(jakemac): Support custom elements that extend html elements which
     // have url-like attributes. This probably means keeping a list of which
     // html elements support each url-like attribute.
     if (!isCustomTagName(node.localName)) {
       node.attributes.forEach((name, value) {
         if (_urlAttributes.contains(name)) {
           if (value != '' && !value.trim().startsWith('{{')) {
             node.attributes[name] = _newUrl(value, node.sourceSpan);
+            changed = changed || value != node.attributes[name];
           }
         }
       });
     }
     if (node.localName == 'style') {
       node.text = visitCss(node.text);
+      changed = true;
     } else if (node.localName == 'script' &&
         node.attributes['type'] == TYPE_DART &&
         !node.attributes.containsKey('src')) {
       // TODO(jmesserly): we might need to visit JS too to handle ES Harmony
       // modules.
       node.text = visitInlineDart(node.text);
+      changed = true;
     }
-    super.visitElement(node);
+    return super.visitElement(node);
   }
 
   static final _URL = new RegExp(r'url\(([^)]*)\)', multiLine: true);
   static final _QUOTE = new RegExp('["\']', multiLine: true);
 
   /// Visit the CSS text and replace any relative URLs so we can inline it.
   // Ported from:
   // https://github.com/Polymer/vulcanize/blob/c14f63696797cda18dc3d372b78aa3378acc691f/lib/vulcan.js#L149
   // TODO(jmesserly): use csslib here instead? Parsing with RegEx is sadness.
   // Maybe it's reliable enough for finding URLs in CSS? I'm not sure.
@@ skipping 101 matching lines @@
 /// When inlining <link rel="stylesheet"> tags copy over all attributes to the
 /// style tag except these ones.
 const IGNORED_LINKED_STYLE_ATTRS =
     const ['charset', 'href', 'href-lang', 'rel', 'rev'];
 
 /// Global RegExp objects for validating generated library names.
 final INVALID_LIB_CHARS_REGEX = new RegExp('[^a-z0-9_]');
 final NUM_REGEX = new RegExp('[0-9]');
 
 _getSpan(SourceFile file, AstNode node) => file.span(node.offset, node.end);