Cleanup and fixes to some dart:io files

tests/standalone/io/http_headers_test.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.
 
 #import('dart:math');
 
 #source("../../../runtime/bin/input_stream.dart");
 #source("../../../runtime/bin/output_stream.dart");
 #source("../../../runtime/bin/chunked_stream.dart");
 #source("../../../runtime/bin/string_stream.dart");
@@ skipping 370 matching lines @@
 }
 
 void testInvalidCookie() {
   Expect.throws(() => new _Cookie.fromSetCookieValue(""));
   Expect.throws(() => new _Cookie.fromSetCookieValue("="));
   Expect.throws(() => new _Cookie.fromSetCookieValue("=xxx"));
   Expect.throws(() => new _Cookie.fromSetCookieValue("xxx"));
   Expect.throws(() => new _Cookie.fromSetCookieValue("xxx=yyy; expires=12 jan 2013"));
 }
 
+void testHeaderLists() {
+  HttpHeaders.GENERAL_HEADERS.forEach((x) => null);
+  HttpHeaders.ENTITY_HEADERS.forEach((x) => null);
+  HttpHeaders.RESPONSE_HEADERS.forEach((x) => null);
+  HttpHeaders.REQUEST_HEADERS.forEach((x) => null);
+}
+
 main() {
   testMultiValue();
   testDate();
   testExpires();
   testIfModifiedSince();
   testHost();
   testEnumeration();
   testHeaderValue();
   testContentType();
   testContentTypeCache();
   testCookie();
   testInvalidCookie();
+  testHeaderLists();
 }