Deprecate publicly-visible properties on Style in path.

pkg/path/lib/src/style/url.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 path.style.url;
 
-import '../style.dart';
+import '../internal_style.dart';
 
 /// The style for URL paths.
-class UrlStyle extends Style {
+class UrlStyle extends InternalStyle {
   UrlStyle();
 
   final name = 'url';
   final separator = '/';
   final separatorPattern = new RegExp(r'/');
   final needsSeparatorPattern = new RegExp(
       r"(^[a-zA-Z][-+.a-zA-Z\d]*://|[^/])$");
   final rootPattern = new RegExp(r"[a-zA-Z][-+.a-zA-Z\d]*://[^/]*");
   final relativeRootPattern = new RegExp(r"^/");
 
   String pathFromUri(Uri uri) => uri.toString();
 
   Uri relativePathToUri(String path) => Uri.parse(path);
   Uri absolutePathToUri(String path) => Uri.parse(path);
 }