Remove usage of dart:json.

pkg/oauth2/test/credentials_test.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 credentials_test;
 
 import 'dart:async';
-import 'dart:json' as JSON;
+import 'dart:convert';
 
 import 'package:http/http.dart' as http;
 import 'package:oauth2/oauth2.dart' as oauth2;
 import 'package:unittest/unittest.dart';
 
 import 'utils.dart';
 
 final Uri tokenEndpoint = Uri.parse('http://example.com/token');
 
 ExpectClient httpClient;
@@ skipping 48 matching lines @@
       expect(request.method, equals('POST'));
       expect(request.url.toString(), equals(tokenEndpoint.toString()));
       expect(request.bodyFields, equals({
         "grant_type": "refresh_token",
         "refresh_token": "refresh token",
         "scope": "scope1 scope2",
         "client_id": "identifier",
         "client_secret": "secret"
       }));
 
-      return new Future.value(new http.Response(JSON.stringify({
+      return new Future.value(new http.Response(JSON.encode({
         'access_token': 'new access token',
         'token_type': 'bearer',
         'refresh_token': 'new refresh token'
       }), 200, headers: {'content-type': 'application/json'}));
     });
 
 
     expect(credentials.refresh('identifier', 'secret', httpClient: httpClient)
         .then((credentials) {
       expect(credentials.accessToken, equals('new access token'));
       expect(credentials.refreshToken, equals('new refresh token'));
     }), completes);
   });
 
   test("uses the old refresh token if a new one isn't provided", () {
     var credentials = new oauth2.Credentials(
         'access token', 'refresh token', tokenEndpoint);
     expect(credentials.canRefresh, true);
 
     httpClient.expectRequest((request) {
       expect(request.method, equals('POST'));
       expect(request.url.toString(), equals(tokenEndpoint.toString()));
       expect(request.bodyFields, equals({
         "grant_type": "refresh_token",
         "refresh_token": "refresh token",
         "client_id": "identifier",
         "client_secret": "secret"
       }));
 
-      return new Future.value(new http.Response(JSON.stringify({
+      return new Future.value(new http.Response(JSON.encode({
         'access_token': 'new access token',
         'token_type': 'bearer'
       }), 200, headers: {'content-type': 'application/json'}));
     });
 
 
     expect(credentials.refresh('identifier', 'secret', httpClient: httpClient)
         .then((credentials) {
       expect(credentials.accessToken, equals('new access token'));
       expect(credentials.refreshToken, equals('refresh token'));
     }), completes);
   });
 
   group("fromJson", () {
     oauth2.Credentials fromMap(Map map) =>
-      new oauth2.Credentials.fromJson(JSON.stringify(map));
+      new oauth2.Credentials.fromJson(JSON.encode(map));
 
     test("should load the same credentials from toJson", () {
       var expiration = new DateTime.now().subtract(new Duration(hours: 1));
       var credentials = new oauth2.Credentials(
           'access token', 'refresh token', tokenEndpoint, ['scope1', 'scope2'],
           expiration);
       var reloaded = new oauth2.Credentials.fromJson(credentials.toJson());
 
       expect(reloaded.accessToken, equals(credentials.accessToken));
       expect(reloaded.refreshToken, equals(credentials.refreshToken));
@@ skipping 35 matching lines @@
       expect(() => fromMap({"accessToken": "foo", "scopes": 12}),
           throwsFormatException);
     });
 
     test("should throw a FormatException if expiration is not an int", () {
       expect(() => fromMap({"accessToken": "foo", "expiration": "12"}),
           throwsFormatException);
     });
   });
 }