fixes #182, avoid injecting a duplicate link rel=stylesheet

lib/src/codegen/html_codegen.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.
 
 library dev_compiler.src.codegen.html_codegen;
 
 import 'package:html/dom.dart';
 import 'package:html/parser.dart' show parseFragment;
 import 'package:logging/logging.dart' show Logger;
 import 'package:path/path.dart' as path;
@@ skipping 25 matching lines @@
     _log.warning(s.sourceSpan.message(
         'unexpected script. Only one Dart script tag allowed '
         '(see https://github.com/dart-lang/dart-dev-compiler/issues/53).',
         color: options.useColors ? colorOf('warning') : false));
     s.remove();
   });
 
   if (options.outputDart) return '${document.outerHtml}\n';
 
   var libraries = [];
-  var resources = [];
+  var resources = new Set();
   visitInPostOrder(root, (n) {
     if (n is DartSourceNode) libraries.add(n);
     if (n is ResourceSourceNode) resources.add(n);
   }, includeParts: false);
 
-  String mainLibraryName;
+  root.htmlResourceNodes.forEach((element, resource) {
+    // Make sure we don't try and add this node again.
+    resources.remove(resource);
+
+    var resourcePath = resourceOutputPath(resource.uri, root.uri);
+    if (resource.cachingHash != null) {
+      resourcePath = _addHash(resourcePath, resource.cachingHash);
+    }
+    var attrs = element.attributes;
+    if (attrs.containsKey('href')) {
+      attrs['href'] = resourcePath;
+    } else if (attrs.containsKey('src')) {
+      attrs['src'] = resourcePath;
+    }
+  });
+
   var fragment = new DocumentFragment();
   for (var resource in resources) {
     var resourcePath = resourceOutputPath(resource.uri, root.uri);
     var ext = path.extension(resourcePath);
     if (resource.cachingHash != null) {
       resourcePath = _addHash(resourcePath, resource.cachingHash);
     }
-    if (ext == '.css') {
-      fragment.nodes.add(_cssInclude(resourcePath));
-    } else if (ext == '.js') {
+    if (ext == '.js') {
       fragment.nodes.add(_libraryInclude(resourcePath));
+    } else if (ext == '.css') {
+      var stylesheetLink = '<link rel="stylesheet" href="$resourcePath">\n';
+      fragment.nodes.add(parseFragment(stylesheetLink));
     }
   }
+
+  String mainLibraryName;
   for (var lib in libraries) {
     var info = lib.info;
     if (info == null) continue;
     if (info.isEntry) mainLibraryName = jsLibraryName(info.library);
     var jsPath = jsOutputPath(info, root.uri);
     if (lib.cachingHash != null) {
       jsPath = _addHash(jsPath, lib.cachingHash);
     }
     fragment.nodes.add(_libraryInclude(jsPath));
   }
   fragment.nodes.add(_invokeMain(mainLibraryName));
   scripts[0].replaceWith(fragment);
   return '${document.outerHtml}\n';
 }
 
 /// A script tag that loads the .js code for a compiled library.
 Node _libraryInclude(String jsUrl) =>
     parseFragment('<script src="$jsUrl"></script>\n');
 
-/// A tag that loads the .css code.
-Node _cssInclude(String cssUrl) =>
-    parseFragment('<link rel="stylesheet" href="$cssUrl">\n');
-
 /// A script tag that invokes the main function on the entry point library.
 Node _invokeMain(String mainLibraryName) {
   var code = mainLibraryName == null
       ? 'console.error("dev_compiler error: main was not generated");'
       // TODO(vsm): Can we simplify this?
       // See: https://github.com/dart-lang/dev_compiler/issues/164
       : '_isolate_helper.startRootIsolate($mainLibraryName.main, []);';
   return parseFragment('<script>$code</script>\n');
 }
 
 /// Convert the outputPath to include the hash in it. This function is the
 /// reverse of what the server does to determine whether a request needs to have
 /// cache headers added to it.
 _addHash(String outPath, String hash) {
   // (the ____ prefix makes it look better in the web inspector)
   return '$outPath?____cached=$hash';
 }
 
 final _log = new Logger('dev_compiler.src.codegen.html_codegen');