Add FileSystemEntity.absolutePath and .isAbsolute properties.

sdk/lib/io/file_system_entity.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 FileSystemEntityType {
   static const FILE = const FileSystemEntityType._internal(0);
   static const DIRECTORY = const FileSystemEntityType._internal(1);
   static const LINK = const FileSystemEntityType._internal(2);
@@ skipping 325 matching lines @@
     request[2] = path2;
     return service.call(request).then((response) {
       if (_isErrorResponse(response)) {
         throw _exceptionFromResponse(response,
             "Error in FileSystemEntity.identical($path1, $path2)", "");
       }
       return response;
     });
   }
 
+  static final RegExp _absoluteWindowsPathPattern =
+      new RegExp(r'^(\\\\|[a-zA-Z]:[/\\])');
+
+  /**
+   * Returns a [bool] indicating whether this object's path is absolute.
+   *
+   * On Windows, a path is absolute if it starts with \\ or a drive letter
+   * between a and z (upper or lower case) followed by :\ or :/.
+   * On non-Windows, a path is absolute if it starts with /.
+   */
+  bool get isAbsolute {
+    if (Platform.isWindows) {
+      return path.startsWith(_absoluteWindowsPathPattern);
+    } else {
+      return path.startsWith('/');
+    }
+  }
+
+  /**
+   * Returns a [FileSystemEntity] whose path is the absolute path to [this].
+   * The type of the returned instance is the type of [this].
+   *
+   * The absolute path is computed by prefixing
+   * a relative path with the current working directory, and returning
+   * an absolute path unchanged.
+   */
+  FileSystemEntity get absolute;
+
+  String get _absolutePath {
+    if (isAbsolute) return path;
+    String current = Directory.current.path;
+    if (current.endsWith('/') ||
+        (Platform.isWindows && current.endsWith('\\'))) {
+      return '$current$path';
+    } else {
+      return '$current${Platform.pathSeparator}$path';
+    }
+  }
+
 
   /**
    * Synchronously checks whether two paths refer to the same object in the
    * file system.
    *
    * Comparing a link to its target returns false, as does comparing two links
    * that point to the same target.  To check the target of a link, use
    * Link.target explicitly to fetch it.  Directory links appearing
    * inside a path are followed, though, to find the file system object.
    *
@@ skipping 224 matching lines @@
   }
 }
 
 
 abstract class _FileSystemWatcher {
   external factory _FileSystemWatcher(String path, int events, bool recursive);
   external static bool get isSupported;
 
   Stream<FileSystemEvent> get stream;
 }