Change fromString constructor to parse static method

pkg/http/lib/src/request.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.
 
 library request;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:typed_data';
 import 'dart:uri';
@@ skipping 136 matching lines @@
   ByteStream finalize() {
     super.finalize();
     return new ByteStream.fromBytes(bodyBytes);
   }
 
   /// The `Content-Type` header of the request (if it exists) as a
   /// [ContentType].
   ContentType get _contentType {
     var contentType = headers[HttpHeaders.CONTENT_TYPE];
     if (contentType == null) return null;
-    return new ContentType.fromString(contentType);
+    return ContentType.parse(contentType);
   }
 
   set _contentType(ContentType value) {
     headers[HttpHeaders.CONTENT_TYPE] = value.toString();
   }
 
   /// Throw an error if this request has been finalized.
   void _checkFinalized() {
     if (!finalized) return;
     throw new StateError("Can't modify a finalized Request.");
   }
 }