Add FileSystemEntity.absolutePath and .isAbsolute properties.

sdk/lib/io/link.dart

Index: sdk/lib/io/link.dart
diff --git a/sdk/lib/io/link.dart b/sdk/lib/io/link.dart
index 3df3fc9f1d5692534f1556aa1b69dae5303b7a8c..83cd22379a1ad6f4556aec92b22ae5c741deb1a1 100644
--- a/sdk/lib/io/link.dart
+++ b/sdk/lib/io/link.dart
@@ -85,6 +85,15 @@ abstract class Link implements FileSystemEntity {
   Link renameSync(String newPath);
 
   /**
+   * Returns a [Link] instance whose path is the absolute path to [this].
+   *
+   * The absolute path is computed by prefixing
+   * a relative path with the current working directory, and returning
+   * an absolute path unchanged.
+   */
+  Link get absolute;
+
+  /**
    * Gets the target of the link. Returns a future that completes with
    * the path to the target.
    *
@@ -127,6 +136,8 @@ class _Link extends FileSystemEntity implements Link {
 
   bool existsSync() => FileSystemEntity.isLinkSync(path);
 
+  Link get absolute => new Link(_absolutePath);
+
   Future<FileStat> stat() => FileStat.stat(path);
 
   FileStat statSync() => FileStat.statSync(path);