Change fromString constructor to parse static method

tests/standalone/io/http_auth_digest_test.dart

 // Copyright (c) 2013, 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 "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:crypto';
 import 'dart:io';
 import 'dart:isolate';
 import 'dart:uri';
@@ skipping 47 matching lines @@
           response.headers.set(HttpHeaders.WWW_AUTHENTICATE, authHeader);
           unauthCount++;
         }
 
         var response = request.response;
         if (request.headers[HttpHeaders.AUTHORIZATION] != null) {
           Expect.equals(1, request.headers[HttpHeaders.AUTHORIZATION].length);
           String authorization =
             request.headers[HttpHeaders.AUTHORIZATION][0];
           HeaderValue header =
-              new HeaderValue.fromString(
+              HeaderValue.parse(
                   authorization, parameterSeparator: ",");
           if (header.value == "basic") {
             sendUnauthorizedResponse(response);
           } else if (!useNextNonce && nonceCount == nonceStaleAfter) {
             nonce = "87654321";
             nonceCount = 0;
             sendUnauthorizedResponse(response, stale: true);
           } else {
             var uri = header.parameters["uri"];
             var qop = header.parameters["qop"];
@@ skipping 305 matching lines @@
   testAuthenticateCallback(null, null);
   testAuthenticateCallback("MD5", null);
   testAuthenticateCallback("MD5", "auth");
   testAuthenticateCallback("MD5", "auth-int");
   testStaleNonce();
   testNextNonce();
   // These teste are not normally run. They can be used for locally
   // testing with another web server (e.g. Apache).
   //testLocalServerDigest();
 }