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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
zoom_controller_->SetZoomLevel(level);
}
double WebContents::GetZoomLevel() {
  return zoom_controller_->GetZoomLevel();
}
void WebContents::SetZoomFactor(double factor) {
  auto level = content::ZoomFactorToZoomLevel(factor);
  SetZoomLevel(level);
}
double WebContents::GetZoomFactor() {
  auto level = GetZoomLevel();
  return content::ZoomLevelToZoomFactor(level);
}
void WebContents::OnSetTemporaryZoomLevel(double level,
                                          IPC::Message* reply_msg) {
  zoom_controller_->SetTemporaryZoomLevel(level);
  double new_level = zoom_controller_->GetZoomLevel();
  AtomViewHostMsg_SetTemporaryZoomLevel::WriteReplyParams(reply_msg, new_level);
  Send(reply_msg);
}
void WebContents::OnGetZoomLevel(IPC::Message* reply_msg) {