Merge the dart:uri library into dart:core and update the Uri class

pkg/oauth2/test/authorization_code_grant_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 authorization_code_grant_test;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:json' as JSON;
-import 'dart:uri';
 
 import 'package:unittest/unittest.dart';
 import 'package:http/http.dart' as http;
 import 'package:http/testing.dart';
 import 'package:oauth2/oauth2.dart' as oauth2;
 
 import 'utils.dart';
 
 final redirectUrl = Uri.parse('http://example.com/redirect');
 
@@ skipping 184 matching lines @@
       });
 
       expect(grant.handleAuthorizationCode('auth code'),
           completion(predicate((client) {
             expect(client.credentials.accessToken, equals('access token'));
             return true;
           })));
     });
   });
 }