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

chrome/browser/ui/views/select_file_dialog_extension.cc

Index: chrome/browser/ui/views/select_file_dialog_extension.cc
diff --git a/chrome/browser/ui/views/select_file_dialog_extension.cc b/chrome/browser/ui/views/select_file_dialog_extension.cc
index dd5b8ba5f825e98018200857f27d2d017bb498fa..0f9cbfbcc634d3180de859d45d09337eed3f5e8b 100644
--- a/chrome/browser/ui/views/select_file_dialog_extension.cc
+++ b/chrome/browser/ui/views/select_file_dialog_extension.cc
@@ -313,8 +313,10 @@ void SelectFileDialogExtension::SelectFileImpl(
   }
 
   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();
   }