Fix checeked mode errors in previous commits

tests/standalone/io/http_parser_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';
 import 'dart:scalarlist';
 
 part '../../../sdk/lib/io/http.dart';
 part '../../../sdk/lib/io/http_headers.dart';
 part '../../../sdk/lib/io/http_parser.dart';
@@ skipping 59 matching lines @@
       httpParser.dataEnd = (close) {
         Expect.isFalse(close);
         dataEndCalled = true;
       };
       httpParser.closed = () { };
 
       headersCompleteCalled = false;
       dataEndCalled = false;
       method = null;
       uri = null;
-      headers = new Map();
+      headers = null;
       bytesReceived = 0;
     }
 
     void testWrite(List<int> requestData, [int chunkSize = -1]) {
       if (chunkSize == -1) chunkSize = requestData.length;
       reset();
       int written = 0;
       int unparsed;
       for (int pos = 0; pos < requestData.length; pos += chunkSize) {
         int remaining = requestData.length - pos;
@@ skipping 124 matching lines @@
         dataEndCalled = true;
         dataEndClose = close;
       };
       httpParser.closed = () { };
 
       headersCompleteCalled = false;
       dataEndCalled = false;
       dataEndClose = null;
       statusCode = -1;
       reasonPhrase = null;
-      headers = new Map();
+      headers = null;
       bytesReceived = 0;
     }
 
     void testWrite(List<int> requestData, [int chunkSize = -1]) {
       if (chunkSize == -1) chunkSize = requestData.length;
       reset();
       int written = 0;
       int unparsed;
       for (int pos = 0; pos < requestData.length; pos += chunkSize) {
         int remaining = requestData.length - pos;
@@ skipping 617 matching lines @@
 0123456789012345678901234567890\r
 0\r\n\r\n""";
     _testParseInvalidResponse(response);
   }
 }
 
 
 void main() {
   HttpParserTest.runAllTests();
 }