Validate headers when added to HttpHeaders.

sdk/lib/io/http_parser.dart

Index: sdk/lib/io/http_parser.dart
diff --git a/sdk/lib/io/http_parser.dart b/sdk/lib/io/http_parser.dart
index 258bfc63e89af294485d570800497ecc3ab4a242..d941aa40b63deef9958a9596286b596d2d55188b 100644
--- a/sdk/lib/io/http_parser.dart
+++ b/sdk/lib/io/http_parser.dart
@@ -912,10 +912,15 @@ class _HttpParser extends Stream<_HttpIncoming> {
     _index = null;
   }
 
-  bool _isTokenChar(int byte) {
+  static bool _isTokenChar(int byte) {
     return byte > 31 && byte < 128 && !_Const.SEPARATOR_MAP[byte];
   }
 
+  static bool _isValueChar(int byte) {
+    return (byte > 31 && byte < 128) || (byte == _CharCode.SP) ||
+        (byte == _CharCode.HT);
+  }
+
   static List<String> _tokenizeFieldValue(String headerValue) {
     List<String> tokens = new List<String>();
     int start = 0;