### Problem Description
I use ubuntu linux. my system language is Chinese, but the dialog button labels is English by default. I found the buttonLabel option from the API to set the label of the save or open button, but the label of the cancel button is not supported.

### Proposed Solution
Support customizing cancel button label in Open and Save dialogs

shell/browser/ui/file_dialog_gtk.cc
gtk_window_set_modal(GTK_WINDOW(dialog_), TRUE);
    }
    if (action == GTK_FILE_CHOOSER_ACTION_SAVE)
      gtk_file_chooser_set_do_overwrite_confirmation(GTK_FILE_CHOOSER(dialog_),
                                                     TRUE);
    if (action != GTK_FILE_CHOOSER_ACTION_OPEN)
      gtk_file_chooser_set_create_folders(GTK_FILE_CHOOSER(dialog_), TRUE);
    if (!settings.default_path.empty()) {
      if (base::DirectoryExists(settings.default_path)) {
        gtk_file_chooser_set_current_folder(
            GTK_FILE_CHOOSER(dialog_), settings.default_path.value().c_str());
      } else {
        if (settings.default_path.IsAbsolute()) {
          gtk_file_chooser_set_current_folder(
              GTK_FILE_CHOOSER(dialog_),
              settings.default_path.DirName().value().c_str());
        }
        gtk_file_chooser_set_current_name(
            GTK_FILE_CHOOSER(dialog_),
            settings.default_path.BaseName().value().c_str());
      }
    }
    if (!settings.filters.empty())
      AddFilters(settings.filters);
    preview_ = gtk_image_new();
    g_signal_connect(dialog_, "update-preview",
                     G_CALLBACK(OnUpdatePreviewThunk), this);
    gtk_file_chooser_set_preview_widget(GTK_FILE_CHOOSER(dialog_), preview_);
  }
  ~FileChooserDialog() {