Re-apply "Add a non-dart:io WebSocket implementation to http_parser."

pkg/http_parser/lib/http_parser.dart

 // Copyright (c) 2014, 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 http_parser;
 
 import 'package:string_scanner/string_scanner.dart';
 
 export 'src/media_type.dart';
+export 'src/web_socket.dart';
 
 const _WEEKDAYS = const ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"];
 const _MONTHS = const ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug",
     "Sep", "Oct", "Nov", "Dec"];
 
 final _shortWeekdayRegExp = new RegExp(r"Mon|Tue|Wed|Thu|Fri|Sat|Sun");
 final _longWeekdayRegExp =
     new RegExp(r"Monday|Tuesday|Wednesday|Thursday|Friday|Saturday|Sunday");
 final _monthRegExp =
     new RegExp(r"Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec");
@@ skipping 126 matching lines @@
 DateTime _makeDateTime(int year, int month, int day, DateTime time) {
   var dateTime = new DateTime.utc(
       year, month, day, time.hour, time.minute, time.second);
 
   // If [day] was too large, it will cause [month] to overflow.
   if (dateTime.month != month) {
     throw new FormatException("invalid day '$day' for month '$month'.");
   }
   return dateTime;
 }