Fix HTTP library issues reported by dart2js

runtime/bin/http_parser.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.
 
 // Global constants.
 class _Const {
   // Bytes for "HTTP/1.0".
   static final HTTP10 = const [72, 84, 84, 80, 47, 49, 46, 48];
   // Bytes for "HTTP/1.1".
   static final HTTP11 = const [72, 84, 84, 80, 47, 49, 46, 49];
@@ skipping 487 matching lines @@
 
   int _expectHexDigit(int byte) {
     if (0x30 <= byte && byte <= 0x39) {
       return byte - 0x30;  // 0 - 9
     } else if (0x41 <= byte && byte <= 0x46) {
       return byte - 0x41 + 10;  // A - F
     } else if (0x61 <= byte && byte <= 0x66) {
       return byte - 0x61 + 10;  // a - f
     } else {
       throw new HttpParserException("Failed to parse HTTP");
-      return 0;
     }
   }
 
   int _state;
   int _httpVersionIndex;
   int _messageType;
   StringBuffer _method_or_status_code;
   StringBuffer _uri_or_reason_phrase;
   StringBuffer _headerField;
   StringBuffer _headerValue;
@@ skipping 15 matching lines @@
   Function dataEnd;
   Function error;
 }
 
 
 class HttpParserException implements Exception {
   const HttpParserException([String this.message = ""]);
   String toString() => "HttpParserException: $message";
   final String message;
 }