Fix Directory.create(recursive: true) for non-existing paths.

sdk/lib/io/directory_impl.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.
 
 part of dart.io;
 
 class _Directory implements Directory {
   static const CREATE_REQUEST = 0;
   static const DELETE_REQUEST = 1;
   static const EXISTS_REQUEST = 2;
@@ skipping 34 matching lines @@
     if (_path is !String) {
       throw new ArgumentError();
     }
     var result = _exists(_path);
     if (result is OSError) {
       throw new DirectoryIOException("Exists failed", _path, result);
     }
     return (result == 1);
   }
 
+  // Compute the index of the first directory in the list that exists. If
+  // none of the directories exist dirsToCreate.length is returned.
   Future<int> _computeExistingIndex(List dirsToCreate) {
     var future;
+    var notFound = dirsToCreate.length;
     for (var i = 0; i < dirsToCreate.length; i++) {
       if (future == null) {
-        future = dirsToCreate[i].exists().transform((e) => e ? i : -1);
+        future = dirsToCreate[i].exists().transform((e) => e ? i : notFound);
       } else {
         future = future.chain((index) {
-          if (index != -1) {
+          if (index != notFound) {
             return new Future.immediate(index);
           }
-          return dirsToCreate[i].exists().transform((e) => e ? i : -1);
+          return dirsToCreate[i].exists().transform((e) => e ? i : notFound);
         });
       }
     }
     if (future == null) {
-      return new Future.immediate(-1);
+      return new Future.immediate(notFound);
     } else {
       return future;
     }
   }
 
   Future<Directory> createRecursively() {
     if (_path is !String) {
       throw new ArgumentError();
     }
     var path = new Path.fromNative(_path);
@@ skipping 259 matching lines @@
     } else {
       throw e;
     }
   }
 
   Function _onDir;
   Function _onFile;
   Function _onDone;
   Function _onError;
 }