Open/save dialog assumes the defaultPath parameter without '/' as a default file name.

chrome/browser/ui/views/select_file_dialog_extension.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/views/select_file_dialog_extension.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
@@ skipping 295 matching lines @@
   // possible. If there is no tab contents use a tab_id of 0. A dialog without
   // an associated tab contents will be shown fully screen; only one at a time
   // is allowed in this state.
   int32 tab_id = tab ? tab->restore_tab_helper()->session_id().id() : 0;
   if (PendingExists(tab_id)) {
     DLOG(WARNING) << "Pending dialog exists with id " << tab_id;
     return;
   }
 
   FilePath virtual_path;
-  if (!file_manager_util::ConvertFileToRelativeFileSystemPath(
+  if (file_manager_util::ConvertFileToRelativeFileSystemPath(
           profile_, default_path, &virtual_path)) {
+    virtual_path = FilePath("/").Append(virtual_path);
+  } else {
     virtual_path = default_path.BaseName();
   }
 
   has_multiple_file_type_choices_ =
       file_types ? file_types->extensions.size() > 1 : true;
 
   GURL file_browser_url = file_manager_util::GetFileBrowserUrlWithParams(
       type, title, virtual_path, file_types, file_type_index,
       default_extension);
 
@@ skipping 13 matching lines @@
   }
 
   // Connect our listener to FileDialogFunction's per-tab callbacks.
   AddPending(tab_id);
 
   extension_dialog_ = dialog;
   params_ = params;
   tab_id_ = tab_id;
   owner_window_ = owner_window;
 }