fix webui for sdk 0.8.7

test/testing.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 definitions used for setting up the test environment. */
 library testing;
 
 import 'dart:async';
 import 'dart:io';
 
@@ skipping 85 matching lines @@
 
   Future readTextOrBytes(String filename) => readText(filename);
 
   Future<String> readText(String path) {
     readCount[path] = readCount.putIfAbsent(path, () => 0) + 1;
     var file = _files[path];
     if (file != null) {
       return new Future.value(file);
     } else {
       return new Future.error(
-          new FileException('MockFileSystem: $path not found'));
+          new FileSystemException('MockFileSystem: $path not found'));
     }
   }
 
   // Compiler doesn't call these
   void writeString(String outfile, String text) {}
   Future flush() {}
 }