Switch from interfaces to abstract classes in dart:io.

runtime/bin/path.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.
 
 /**
  * A Path, which is a String interpreted as a sequence of path segments,
  * which are strings, separated by forward slashes.
  * Paths are immutable wrappers of a String, that offer member functions for
  * useful path manipulations and queries.  Joining of paths and normalization
  * interpret '.' and '..' in the usual way.
  */
-interface Path extends Hashable default _Path {
+abstract class Path extends Hashable {
   /**
    * Creates a Path from the String [source].  [source] is used as-is, so if
    * the string does not consist of segments separated by forward slashes, the
-   * behavior may not be as expected.  Paths are immutable, and constant
-   * Path objects may be constructed from constant Strings.
+   * behavior may not be as expected.  Paths are immutable.
    */
-  const Path(String source);
+  factory Path(String source) => new _Path(source);
 
   /**
    * Creates a Path from a String that uses the native filesystem's conventions.
    * On Windows, this converts '\' to '/', and adds a '/' before a drive letter.
    * A path starting with '/c:/' (or any other character instead of 'c') is
    * treated specially.  Backwards links ('..') cannot cancel the drive letter.
    */
-  Path.fromNative(String source);
+  factory Path.fromNative(String source) => new _Path.fromNative(source);
 
   /**
    * Is this path the empty string?
    */
   bool get isEmpty;
 
   /**
    * Is this path an absolute path, beginning with a path separator?
    */
   bool get isAbsolute;
@@ skipping 128 matching lines @@
 
   /**
    * The part of [filename] after the last '.', or '' if [filename]
    * contains no '.'.  If [filename] is '.' or '..', returns ''.
    *
    *     new Path('tiger.svg').extension == 'svg'
    *     new Path('/src/dart/dart_secrets').extension == ''
    */
   String get extension;
 }