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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
PrintSettings* out) {
    mate::Dictionary dict;
    if (!ConvertFromV8(isolate, val, &dict))
      return false;
    dict.Get("silent", &(out->silent));
    dict.Get("printBackground", &(out->print_background));
    return true;
  }
};
template<>
struct Converter<WindowOpenDisposition> {
  static v8::Local<v8::Value> ToV8(v8::Isolate* isolate,