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* Electron version: 1.6.1
* Operating system: macOS

### Expected behavior

navigator.geolocation.getCurrentPosition runs in background

### Actual behavior

the entire UI is frozen

### How to reproduce

```js
    navigator.geolocation.getCurrentPosition((pos) => {
      console.log('POS: ' + pos);
    }, (err) => {
      console.log('Geolocation error: ', err);
    }, {enableHighAccuracy: false});
```
atom/browser/api/atom_api_web_contents.cc
WindowOpenDisposition val) {
    std::string disposition = "other";
    switch (val) {
      case WindowOpenDisposition::CURRENT_TAB:
        disposition = "default";
        break;
      case WindowOpenDisposition::NEW_FOREGROUND_TAB:
        disposition = "foreground-tab";
        break;
      case WindowOpenDisposition::NEW_BACKGROUND_TAB:
        disposition = "background-tab";
        break;
      case WindowOpenDisposition::NEW_POPUP:
      case WindowOpenDisposition::NEW_WINDOW:
        disposition = "new-window";
        break;
      case WindowOpenDisposition::SAVE_TO_DISK:
        disposition = "save-to-disk";
        break;
      default:
        break;
    }
    return mate::ConvertToV8(isolate, disposition);
  }
};
template<>
struct Converter<content::SavePageType> {
  static bool FromV8(v8::Isolate* isolate, v8::Local<v8::Value> val,