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

pkg/oauth2/lib/src/credentials.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;
 
 import 'dart:async';
 import 'dart:json' as JSON;
-import 'dart:uri';
 
 import 'package:http/http.dart' as http;
 
 import 'handle_access_token_response.dart';
 import 'utils.dart';
 
 /// Credentials that prove that a client is allowed to access a resource on the
 /// resource owner's behalf. These credentials are long-lasting and can be
 /// safely persisted across multiple runs of the program.
 ///
@@ skipping 165 matching lines @@
       if (credentials.refreshToken != null) return credentials;
       return new Credentials(
           credentials.accessToken,
           this.refreshToken,
           credentials.tokenEndpoint,
           credentials.scopes,
           credentials.expiration);
     });
   }
 }