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

pkg/http/test/client_test.dart

 // Copyright (c) 2013, 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 client_test;
 
 import 'dart:io';
-import 'dart:uri';
 
 import 'package:http/http.dart' as http;
 import 'package:http/src/utils.dart';
 import 'package:unittest/unittest.dart';
 
 import 'utils.dart';
 
 void main() {
   tearDown(stopServer);
 
@@ skipping 37 matching lines @@
       request.headers[HttpHeaders.CONTENT_TYPE] =
           'application/json; charset=utf-8';
 
       expect(client.send(request), throwsSocketIOException);
 
       request.sink.add('{"hello": "world"}'.codeUnits);
       request.sink.close();
     }), completes);
   });
 }