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### Issue Details

* **Electron Version:**
  * 7.0.0
* **Operating System:**
  * Ubuntu 18.04 (KDE Neon)
* **Last Known Working Electron version:**
  * 6.0.12

### Expected Behavior
dialog.showOpenDialog() should have the default label "Open"
dialog.showSaveDialog() should have the default label "Save"

### Actual Behavior
The labels are erroneously switched.

### Screenshots
<!-- If applicable, add screenshots to help explain your problem. -->
![labels_wrong](https://user-images.githubusercontent.com/14349333/67726433-c03fb500-f9dd-11e9-8a8a-63626e7bde1f.png)

shell/browser/ui/file_dialog_gtk.cc
gtk_widget_destroy(dialog_);
    if (parent_)
      parent_->SetEnabled(true);
  }
  void SetupOpenProperties(int properties) {
    const auto hasProp = [properties](OpenFileDialogProperty prop) {
      return gboolean((properties & prop) != 0);
    };
    auto* file_chooser = GTK_FILE_CHOOSER(dialog());
    gtk_file_chooser_set_select_multiple(file_chooser,
                                         hasProp(OPEN_DIALOG_MULTI_SELECTIONS));
    gtk_file_chooser_set_show_hidden(file_chooser,
                                     hasProp(OPEN_DIALOG_SHOW_HIDDEN_FILES));
  }
  void SetupSaveProperties(int properties) {