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

pkg/http/lib/src/request.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 request;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:typed_data';
-import 'dart:uri';
 
 import 'base_request.dart';
 import 'byte_stream.dart';
 import 'utils.dart';
 
 /// An HTTP request where the entire request body is known in advance.
 class Request extends BaseRequest {
   /// The size of the request body, in bytes. This is calculated from
   /// [bodyBytes].
   ///
@@ skipping 139 matching lines @@
   set _contentType(ContentType value) {
     headers[HttpHeaders.CONTENT_TYPE] = value.toString();
   }
 
   /// Throw an error if this request has been finalized.
   void _checkFinalized() {
     if (!finalized) return;
     throw new StateError("Can't modify a finalized Request.");
   }
 }