Fix map literals from change 17410

pkg/http/lib/src/response.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.
 
 library response;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:scalarlist';
 
@@ skipping 13 matching lines @@
   /// [Encoding.ISO_8859_1] is used by default, as per [RFC 2616][].
   ///
   /// [RFC 2616]: http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html
   String get body => decodeString(bodyBytes, _encodingForHeaders(headers));
 
   /// Creates a new HTTP response with a string body.
   Response(
       String body,
       int statusCode,
       {BaseRequest request,
-       Map<String, String> headers: const <String, String>{},
+       Map<String, String> headers: const {},
        bool isRedirect: false,
        bool persistentConnection: true,
        String reasonPhrase})
     : this.bytes(
         encodeString(body, _encodingForHeaders(headers)),
         statusCode,
         request: request,
         headers: headers,
         isRedirect: isRedirect,
         persistentConnection: persistentConnection,
         reasonPhrase: reasonPhrase);
 
   /// Create a new HTTP response with a byte array body.
   Response.bytes(
       List<int> bodyBytes,
       int statusCode,
       {BaseRequest request,
-       Map<String, String> headers: const <String, String>{},
+       Map<String, String> headers: const {},
        bool isRedirect: false,
        bool persistentConnection: true,
        String reasonPhrase})
     : bodyBytes = toUint8List(bodyBytes),
       super(
         statusCode,
         bodyBytes.length,
         request: request,
         headers: headers,
         isRedirect: isRedirect,
@@ skipping 22 matching lines @@
 Encoding _encodingForHeaders(Map<String, String> headers) =>
   encodingForCharset(_contentTypeForHeaders(headers).charset);
 
 /// Returns the [ContentType] object for the given headers. Defaults to
 /// `application/octet-stream`.
 ContentType _contentTypeForHeaders(Map<String, String> headers) {
   var contentType = headers[HttpHeaders.CONTENT_TYPE];
   if (contentType != null) return new ContentType.fromString(contentType);
   return new ContentType("application", "octet-stream");
 }