append html imports before the dart script tag

lib/build/web_components.dart

 // Copyright (c) 2015, 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.
 
 /// Transformer used for pub serve and pub build
 library web_components.build.web_components;
 
 import 'dart:async';
 import 'package:barback/barback.dart';
 import 'package:code_transformers/assets.dart';
@@ skipping 14 matching lines @@
     {List<InitializerPlugin> extraPlugins: const []}) {
   var htmlImportRecorder = new HtmlImportAnnotationRecorder();
   var plugins = [htmlImportRecorder]..addAll(extraPlugins);
 
   // Bootstrap the application using the `initialize` package and our
   // plugins.
   var initializeBootstrap = generateBootstrapFile(
       resolver, transform, scriptId, newScriptId,
       errorIfNotFound: false, plugins: plugins);
 
-  // Add all seen imports to the document.
+  // Add all seen imports to the document, before the first dart script tag if
+  // it exists.
+  var dartScript =
+      document.head.querySelector('script[type="application/dart"]');
   for (var importPath in htmlImportRecorder.importPaths) {
-    document.head.append(new dom.Element.tag('link')
-      ..attributes = {'rel': 'import', 'href': importPath,});
+    var import = new dom.Element.tag('link')
+      ..attributes = {'rel': 'import', 'href': importPath,};
+    document.head.insertBefore(import, dartScript);
   }
 
   return initializeBootstrap;
 }
 
 /// A [Transformer] which runs the `initialize` transformer with
 /// some special plugins and also inlines the html imports.
 class WebComponentsTransformer extends Transformer {
   final Resolvers _resolvers;
   TransformOptions options;
@@ skipping 75 matching lines @@
             from: path.url.dirname(primaryInput.id.path));
 
         // Output the new document and bootstrap file.
         transform
             .addOutput(new Asset.fromString(primaryInput.id, doc.outerHtml));
         transform.addOutput(bootstrap);
       });
     });
   }
 }