Fix listing of '' and '/'.

sdk/lib/io/directory_impl.dart

Index: sdk/lib/io/directory_impl.dart
diff --git a/sdk/lib/io/directory_impl.dart b/sdk/lib/io/directory_impl.dart
index 73f7de8ebfc18be7cf97e5bf66513f83b5d03f71..dd789c7235ba003951a57ab9b5479df3fa64c4a8 100644
--- a/sdk/lib/io/directory_impl.dart
+++ b/sdk/lib/io/directory_impl.dart
@@ -213,7 +213,7 @@ class _Directory extends FileSystemEntity implements Directory {
   Stream<FileSystemEntity> list({bool recursive: false,
                                  bool followLinks: true}) {
     return new _AsyncDirectoryLister(
-        FileSystemEntity._trimTrailingPathSeparators(path),
+        FileSystemEntity._ensureTrailingPathSeparators(path),
         recursive,
         followLinks).stream;
   }
@@ -223,7 +223,7 @@ class _Directory extends FileSystemEntity implements Directory {
       throw new ArgumentError();
     }
     return _list(
-        FileSystemEntity._trimTrailingPathSeparators(path),
+        FileSystemEntity._ensureTrailingPathSeparators(path),
         recursive,
         followLinks);
   }