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

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:io';
 import 'dart:json' as JSON;
-import 'dart:uri';
 
 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 150 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);
     });
   });
 }