Change fromString constructor to parse static method

sdk/lib/io/http_headers.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.
 
 part of dart.io;
 
 class _HttpHeaders implements HttpHeaders {
   _HttpHeaders(String this.protocolVersion)
       : _headers = new Map<String, List<String>>();
 
@@ skipping 178 matching lines @@
   void set expires(DateTime expires) {
     _checkMutable();
     // Format "Expires" header with date in Greenwich Mean Time (GMT).
     String formatted = _HttpUtils.formatDate(expires.toUtc());
     _set(HttpHeaders.EXPIRES, formatted);
   }
 
   ContentType get contentType {
     var values = _headers["content-type"];
     if (values != null) {
-      return new ContentType.fromString(values[0]);
+      return ContentType.parse(values[0]);
     } else {
       return null;
     }
   }
 
   void set contentType(ContentType contentType) {
     _checkMutable();
     _set(HttpHeaders.CONTENT_TYPE, contentType.toString());
   }
 
@@ skipping 260 matching lines @@
   int _port;
 }
 
 
 class _HeaderValue implements HeaderValue {
   String _value;
   Map<String, String> _parameters;
 
   _HeaderValue([String this._value = "", this._parameters]);
 
-  _HeaderValue.fromString(String value, {parameterSeparator: ";"}) {
+  static _HeaderValue parse(String value, {parameterSeparator: ";"}) {
     // Parse the string.
-    _parse(value, parameterSeparator);
+    var result = new _HeaderValue();
+    result._parse(value, parameterSeparator);
+    return result;
   }
 
   String get value => _value;
 
   Map<String, String> get parameters {
     if (_parameters == null) _parameters = new Map<String, String>();
     return _parameters;
   }
 
   String toString() {
@@ skipping 121 matching lines @@
     if (parameters != null) {
       parameters.forEach((String key, String value) {
         this.parameters[key.toLowerCase()] = value.toLowerCase();
       });
     }
     if (charset != null) {
       this.parameters["charset"] = charset.toLowerCase();
     }
   }
 
-  _ContentType.fromString(String value) : super.fromString(value) {
-    int index = _value.indexOf("/");
-    if (index == -1 || index == (_value.length - 1)) {
-      _primaryType = _value.trim().toLowerCase();
-      _subType = "";
+  _ContentType._();
+
+  static _ContentType parse(String value) {
+    var result = new _ContentType._();
+    result._parse(value, ";");
+    int index = result._value.indexOf("/");
+    if (index == -1 || index == (result._value.length - 1)) {
+      result._primaryType = result._value.trim().toLowerCase();
+      result._subType = "";
     } else {
-      _primaryType = _value.substring(0, index).trim().toLowerCase();
-      _subType = _value.substring(index + 1).trim().toLowerCase();
+      result._primaryType = result._value.substring(0, index).trim().toLowerCase();
+      result._subType = result._value.substring(index + 1).trim().toLowerCase();
     }
+    return result;
   }
 
   String get mimeType => '$primaryType/$subType';
 
   String get primaryType => _primaryType;
 
   String get subType => _subType;
 
   String get charset => parameters["charset"];
 }
@@ skipping 121 matching lines @@
 
   String name;
   String value;
   DateTime expires;
   int maxAge;
   String domain;
   String path;
   bool httpOnly = false;
   bool secure = false;
 }