Remane io_stream_consumer.dart to io_sink and move out all implementation from IOSink to _IOSinkImp…

tests/standalone/io/url_encoding_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.
 
 import "dart:async";
 import "dart:utf";
 
-part '../../../sdk/lib/io/io_stream_consumer.dart';
+part '../../../sdk/lib/io/io_sink.dart';
 part "../../../sdk/lib/io/http.dart";
 part "../../../sdk/lib/io/http_impl.dart";
 part "../../../sdk/lib/io/http_parser.dart";
 part "../../../sdk/lib/io/http_utils.dart";
 part "../../../sdk/lib/io/socket.dart";
 
 void testParseEncodedString() {
   String encodedString = 'foo+bar%20foobar%25%26';
   Expect.equals(_HttpUtils.decodeUrlEncodedString(encodedString),
                 'foo bar foobar%&');
@@ skipping 15 matching lines @@
                               'sqrt2' : '\u221A2',
                               'name'  : 'Franti\u0161ek'}[key]);
   }
   Expect.setEquals(map.keys.toSet(), ['&', '?', 'foo', 'sqrt2', 'name']);
 }
 
 void main() {
   testParseEncodedString();
   testParseQueryString();
 }