Improve how we handle packages/ HTML imports. This resolves better any valid

pkg/polymer/lib/src/loader.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.
 
 part of polymer;
 
 /** Annotation used to automatically register polymer elements. */
 class CustomTag {
   final String tagName;
   const CustomTag(this.tagName);
@@ skipping 120 matching lines @@
   return scripts;
 }
 
 /** All libraries in the current isolate. */
 final _libs = currentMirrorSystem().libraries;
 
 // TODO(sigmund): explore other (cheaper) ways to resolve URIs relative to the
 // root library (see dartbug.com/12612)
 final _rootUri = currentMirrorSystem().isolate.rootLibrary.uri;
 
-final String _packageRoot =
-    path.url.join(path.url.dirname(Uri.parse(window.location.href).path),
-        'packages') + '/';
+final Logger _loaderLog = new Logger('polymer.loader');
 
-final Logger _loaderLog = new Logger('polymer.loader');
+bool _isHttpStylePackageUrl(Uri uri) {
+  var uriPath = uri.path;
+  return uri.scheme == _rootUri.scheme &&
+      // Don't process cross-domain uris.
+      uri.authority == _rootUri.authority &&
+      uriPath.endsWith('.dart') &&
+      (uriPath.contains('/packages/') || uriPath.startsWith('packages/'));
+}
 
 /**
  * Reads the library at [uriString] (which can be an absolute URI or a relative
  * URI from the root library), and:
  *
  *   * If present, invokes any top-level and static functions marked
  *     with the [initMethod] annotation (in the order they appear).
  *
  *   * Registers any [PolymerElement] that is marked with the [CustomTag]
  *     annotation.
  */
 void _loadLibrary(String uriString) {
   var uri = _rootUri.resolve(uriString);
   var lib = _libs[uri];
-  if (uri.path.startsWith(_packageRoot) && uri.path.endsWith('.dart')) {
-    var packageUri =
-        Uri.parse('package:${uri.path.substring(_packageRoot.length)}');
-    var canonicalLib = _libs[packageUri];
+  if (_isHttpStylePackageUrl(uri)) {
+    // Use package: urls if available. This rule here is more permissive than
+    // how we translate urls in polymer-build, but we expect Dartium to limit
+    // the cases where there are differences. The polymer-build issues an error
+    // when using packages/ inside lib without properly stepping out all the way
+    // to the packages folder. If users don't create symlinks in the source
+    // tree, then Dartium will also complain because it won't find the file seen
+    // in an HTML import.
+    var packagePath = uri.path.substring(
+        uri.path.lastIndexOf('packages/') + 'packages/'.length);
+    var canonicalLib = _libs[Uri.parse('package:$packagePath')];
     if (canonicalLib != null) {
       lib = canonicalLib;
     }
   }
 
   if (lib == null) {
     _loaderLog.info('$uri library not found');
     return;
   }
 
@@ skipping 38 matching lines @@
     print("warning: methods marked with @initMethod should take no "
         "arguments, ${method.simpleName} expects some.");
     return;
   }
   obj.invoke(method.simpleName, const []);
 }
 
 class _InitMethodAnnotation {
   const _InitMethodAnnotation();
 }