gracefully degrade with response to client if fail to access client specified dart sdk

pkg/analysis_server/test/protocol_test.dart

 // Copyright (c) 2014, 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 test.protocol;
 
 import 'package:analysis_server/src/protocol.dart';
 import 'package:unittest/matcher.dart';
 import 'package:unittest/unittest.dart';
 import 'dart:convert';
@@ skipping 95 matching lines @@
   }
 
   static void getRequiredParameter_undefined() {
     String name = 'name';
     Request request = new Request('0', '');
     expect(() => request.getRequiredParameter(name), throwsA(new isInstanceOf<RequestFailure>()));
   }
 
   static void fromJson() {
     Request original = new Request('one', 'aMethod');
-    String json = new JsonEncoder(null).convert(original.toJson());
+    String json = JSON.encode(original.toJson());
     Request request = new Request.fromString(json);
     expect(request.id, equals('one'));
     expect(request.method, equals('aMethod'));
   }
 
   static void fromJson_invalidId() {
     String json = '{"id":{"one":"two"},"method":"aMethod","params":{"foo":"bar"}}';
     Request request = new Request.fromString(json);
     expect(request, isNull);
   }
 
   static void fromJson_invalidMethod() {
     String json = '{"id":"one","method":{"boo":"aMethod"},"params":{"foo":"bar"}}';
     Request request = new Request.fromString(json);
     expect(request, isNull);
   }
 
   static void fromJson_invalidParams() {
     String json = '{"id":"one","method":"aMethod","params":"foobar"}';
     Request request = new Request.fromString(json);
     expect(request, isNull);
   }
 
   static void fromJson_withParams() {
     Request original = new Request('one', 'aMethod');
     original.setParameter('foo', 'bar');
-    String json = new JsonEncoder(null).convert(original.toJson());
+    String json = JSON.encode(original.toJson());
     Request request = new Request.fromString(json);
     expect(request.id, equals('one'));
     expect(request.method, equals('aMethod'));
     expect(request.getParameter('foo'), equals('bar'));
   }
 
   static void toJson() {
     Request request = new Request('one', 'aMethod');
     expect(request.toJson(), equals({
       Request.ID : 'one',
@@ skipping 86 matching lines @@
   static void fromJson_withResult() {
     Response original = new Response('myId');
     original.setResult('foo', 'bar');
     Response response = new Response.fromJson(original.toJson());
     expect(response.id, equals('myId'));
     Map<String, Object> result = response.result;
     expect(result.length, equals(1));
     expect(result['foo'], equals('bar'));
   }
 }