fix webui for sdk 0.8.7

lib/component_build.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Common logic to make it easy to create a `build.dart` for your project.
  *
  * The `build.dart` script is invoked automatically by the Editor whenever a
  * file in the project changes. It must be placed in the root of a project
  * (where pubspec.yaml lives) and should be named exactly 'build.dart'.
  *
  * A common `build.dart` would look as follows:
  *
  *     import 'dart:io';
  *     import 'package:web_ui/component_build.dart';
  *
  *     main() => build(new Options().arguments, ['web/index.html']);
  */
 library build_utils;
 
 import 'dart:async';
 import 'dart:io';
-import 'dart:json' as json;
+import 'dart:convert';
 import 'package:args/args.dart';
 
 import 'dwc.dart' as dwc;
 import 'src/utils.dart';
 import 'src/options.dart';
 
 /**
  * Set up 'build.dart' to compile with the dart web components compiler every
  * [entryPoints] listed. On clean commands, the directory where [entryPoints]
  * live will be scanned for generated files to delete them.
@@ skipping 43 matching lines @@
         // We'll set 'out/' as the out folder, unless an output directory was
         // already specified in the command line.
         if (options.outputDir == null) dwcArgs.addAll(['-o', _outDir(file)]);
         dwcArgs.add(file);
         // Chain tasks to that we run one at a time.
         lastTask = lastTask.then((_) => dwc.run(dwcArgs, printTime: printTime,
             shouldPrint: shouldPrint));
         if (machineFormat) {
           lastTask = lastTask.then((res) {
             appendMessage(Map jsonMessage) {
-              var message = json.stringify([jsonMessage]);
+              var message = JSON.encode([jsonMessage]);
               if (shouldPrint) print(message);
               res.messages.add(message);
             }
             // Print for the Editor messages about mappings and generated files
             res.outputs.forEach((out, input) {
               if (out.endsWith(".html") && input != null) {
                 appendMessage({
                   "method": "mapping",
                   "params": {"from": input, "to": out},
                 });
@@ skipping 59 matching lines @@
   if (args["help"]) {
     print('A build script that invokes the web-ui compiler (dwc).');
     print('Usage: dart build.dart [options] [-- [dwc-options]]');
     print('\nThese are valid options expected by build.dart:');
     print(parser.getUsage());
     print('\nThese are valid options expected by dwc:');
     dwc.run(['-h']).then((_) => exit(0));
   }
   return args;
 }