Remove usage of dart:json.

pkg/oauth2/lib/src/handle_access_token_response.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 handle_access_token_response;
 
 import 'dart:io';
-import 'dart:json' as JSON;
+import 'dart:convert';
 
 import 'package:http/http.dart' as http;
 
 import 'credentials.dart';
 import 'authorization_exception.dart';
 
 /// The amount of time, in seconds, to add as a "grace period" for credential
 /// expiration. This allows credential expiration checks to remain valid for a
 /// reasonable amount of time.
 const _EXPIRATION_GRACE = 10;
@@ skipping 13 matching lines @@
 
   var contentType = response.headers['content-type'];
   if (contentType != null) {
     contentType = ContentType.parse(contentType);
   }
   validate(contentType != null && contentType.value == "application/json",
       'content-type was "$contentType", expected "application/json"');
 
   var parameters;
   try {
-    parameters = JSON.parse(response.body);
+    parameters = JSON.decode(response.body);
   } on FormatException catch (e) {
     validate(false, 'invalid JSON');
   }
 
   for (var requiredParameter in ['access_token', 'token_type']) {
     validate(parameters.containsKey(requiredParameter),
         'did not contain required parameter "$requiredParameter"');
     validate(parameters[requiredParameter] is String,
         'required parameter "$requiredParameter" was not a string, was '
         '"${parameters[requiredParameter]}"');
@@ skipping 48 matching lines @@
 
   var contentType = response.headers['content-type'];
   if (contentType != null) {
     contentType = ContentType.parse(contentType);
   }
   validate(contentType != null && contentType.value == "application/json",
       'content-type was "$contentType", expected "application/json"');
 
   var parameters;
   try {
-    parameters = JSON.parse(response.body);
+    parameters = JSON.decode(response.body);
   } on FormatException catch (e) {
     validate(false, 'invalid JSON');
   }
 
   validate(parameters.containsKey('error'),
       'did not contain required parameter "error"');
   validate(parameters["error"] is String,
       'required parameter "error" was not a string, was '
       '"${parameters["error"]}"');
 
@@ skipping 11 matching lines @@
 
 void _validate(
     http.Response response,
     Uri tokenEndpoint,
     bool condition,
     String message) {
   if (condition) return;
   throw new FormatException('Invalid OAuth response for "$tokenEndpoint": '
       '$message.\n\n${response.body}');
 }