Extract an http_parser package from shelf.

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 shelf.util;
+library http_parser;
 
-import 'dart:async';
-
-import 'package:stack_trace/stack_trace.dart';
 import 'package:string_scanner/string_scanner.dart';
 
-/// Like [Future.sync], but wraps the Future in [Chain.track] as well.
-Future syncFuture(callback()) => Chain.track(new Future.sync(callback));
+export 'src/media_type.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 91 matching lines @@
   scanner.expect(_monthRegExp);
   // DateTime uses 1-indexed months.
   return _MONTHS.indexOf(scanner.lastMatch[0]) + 1;
 }
 
 /// Parses an int an enforces that it has exactly [digits] digits.
 int _parseInt(StringScanner scanner, int digits) {
   scanner.expect(_digitRegExp);
   if (scanner.lastMatch[0].length != digits) {
     scanner.error("expected a $digits-digit number.");
-  } else {
-    return int.parse(scanner.lastMatch[0]);
   }
+
+  return int.parse(scanner.lastMatch[0]);
 }
 
 /// Parses an timestamp of the form "HH:MM:SS" on a 24-hour clock.
 DateTime _parseTime(StringScanner scanner) {
   var hours = _parseInt(scanner, 2);
   if (hours >= 24) scanner.error("hours may not be greater than 24.");
   scanner.expect(':');
 
   var minutes = _parseInt(scanner, 2);
   if (minutes >= 60) scanner.error("minutes may not be greater than 60.");
@@ skipping 12 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;
 }