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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_hide(dialog_);
  if (save_promise_) {
    gin_helper::Dictionary dict =
        gin::Dictionary::CreateEmpty(save_promise_->isolate());
    if (response == GTK_RESPONSE_ACCEPT) {
      dict.Set("canceled", false);
      dict.Set("filePath", GetFileName());
    } else {
      dict.Set("canceled", true);
      dict.Set("filePath", base::FilePath());
    }
    save_promise_->ResolveWithGin(dict);
  } else if (open_promise_) {
    gin_helper::Dictionary dict =
        gin::Dictionary::CreateEmpty(open_promise_->isolate());
    if (response == GTK_RESPONSE_ACCEPT) {
      dict.Set("canceled", false);
      dict.Set("filePaths", GetFileNames());
    } else {
      dict.Set("canceled", true);
      dict.Set("filePaths", std::vector<base::FilePath>());
    }
    open_promise_->ResolveWithGin(dict);
  }
  delete this;
}
void FileChooserDialog::AddFilters(const Filters& filters) {