fix webui for sdk 0.8.7

lib/src/compiler.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.
 
 library compiler;
 
 import 'dart:async';
 import 'dart:collection' show SplayTreeMap;
-import 'dart:json' as json;
+import 'dart:convert';
 import 'package:analyzer_experimental/src/generated/ast.dart' show Directive, UriBasedDirective;
 import 'package:csslib/visitor.dart' show StyleSheet, treeToDebugString;
 import 'package:html5lib/dom.dart';
 import 'package:html5lib/parser.dart';
 import 'package:source_maps/span.dart' show Span;
 
 import 'analyzer.dart';
 import 'code_printer.dart';
 import 'dart_parser.dart';
 import 'emitters.dart';
@@ skipping 734 matching lines @@
     if (printer == null) return;
 
     var libPath = _pathMapper.outputLibraryPath(lib);
     var dir = path.dirname(libPath);
     var filename = path.basename(libPath);
     printer.add('\n//# sourceMappingURL=$filename.map');
     printer.build(libPath);
     var sourcePath = dartCodeUrl != null ? dartCodeUrl.resolvedPath : null;
     output.add(new OutputFile(libPath, printer.text, source: sourcePath));
     // Fix-up the paths in the source map file
-    var sourceMap = json.parse(printer.map);
+    var sourceMap = JSON.decode(printer.map);
     var urls = sourceMap['sources'];
     for (int i = 0; i < urls.length; i++) {
       urls[i] = path.relative(urls[i], from: dir);
     }
     output.add(new OutputFile(path.join(dir, '$filename.map'),
-          json.stringify(sourceMap)));
+          JSON.encode(sourceMap)));
   }
 
   _time(String logMessage, String filePath, callback(),
       {bool printTime: false}) {
     var message = new StringBuffer();
     message.write(logMessage);
     var filename = path.basename(filePath);
     for (int i = (60 - logMessage.length - filename.length); i > 0 ; i--) {
       message.write(' ');
     }
@@ skipping 28 matching lines @@
 
 import 'package:web_ui/watcher.dart' as watcher;
 import '$userMainImport' as userMain;
 
 main() {
   watcher.useObservers = $useObservers;
   userMain.main();
   userMain.init_autogenerated();
 }
 """;