Fix directory-listing to return a future on cancel.

runtime/bin/directory_macos.cc

Index: runtime/bin/directory_macos.cc
diff --git a/runtime/bin/directory_macos.cc b/runtime/bin/directory_macos.cc
index 074647fed70cdc525bc1250827dad9bb0516a0f0..feb9a9ca8dec1a7045eaac9bef0a6badd322c3e2 100644
--- a/runtime/bin/directory_macos.cc
+++ b/runtime/bin/directory_macos.cc
@@ -187,14 +187,18 @@ ListType DirectoryListingEntry::Next(DirectoryListing* listing) {
     return kListError;
   }
 
-  if (closedir(reinterpret_cast<DIR*>(lister_)) == -1) {
-    return kListError;
-  }
-
   return kListDone;
 }
 
 
+DirectoryListingEntry::~DirectoryListingEntry() {
+  ResetLink();
+  if (lister_ != 0) {
+    closedir(reinterpret_cast<DIR*>(lister_));
+  }
+}
+
+
 void DirectoryListingEntry::ResetLink() {
   if (link_ != NULL && (parent_ == NULL || parent_->link_ != link_)) {
     delete link_;