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

pkg/http/test/mock_client_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 mock_client_test;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:json' as json;
-import 'dart:uri';
 
 import 'package:http/http.dart' as http;
 import 'package:http/src/utils.dart';
 import 'package:http/testing.dart';
 import 'package:unittest/unittest.dart';
 
 import 'utils.dart';
 
 void main() {
   test('handles a request', () {
@@ skipping 36 matching lines @@
 
   test('handles a request with no body', () {
     var client = new MockClient((request) {
       return new Future.value(new http.Response('you did it', 200));
     });
 
     expect(client.read("http://example.com/foo"),
         completion(equals('you did it')));
   });
 }