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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
blink::WebMouseWheelEvent mouse_wheel_event;
    if (mate::ConvertFromV8(isolate, input_event, &mouse_wheel_event)) {
      host->ForwardWheelEvent(mouse_wheel_event);
      return;
    }
  }
  isolate->ThrowException(v8::Exception::Error(mate::StringToV8(
      isolate, "Invalid event object")));
}
void WebContents::BeginFrameSubscription(mate::Arguments* args) {
  bool only_dirty = false;
  FrameSubscriber::FrameCaptureCallback callback;
  args->GetNext(&only_dirty);
  if (!args->GetNext(&callback)) {
    args->ThrowError();
    return;
  }
  const auto view = web_contents()->GetRenderWidgetHostView();
  if (view) {
    std::unique_ptr<FrameSubscriber> frame_subscriber(new FrameSubscriber(
        isolate(), view, callback, only_dirty));
    view->BeginFrameSubscription(std::move(frame_subscriber));
  }
}
void WebContents::EndFrameSubscription() {
  const auto view = web_contents()->GetRenderWidgetHostView();
  if (view)
    view->EndFrameSubscription();
}
void WebContents::StartDrag(const mate::Dictionary& item,