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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
args->ThrowError("Must specify either 'file' or 'files' option");
  }
}
void WebContents::CapturePage(mate::Arguments* args) {
  gfx::Rect rect;
  base::Callback<void(const gfx::Image&)> callback;
  if (!(args->Length() == 1 && args->GetNext(&callback)) &&
      !(args->Length() == 2 && args->GetNext(&rect)
                            && args->GetNext(&callback))) {
    args->ThrowError();
    return;
  }
  const auto view = web_contents()->GetRenderWidgetHostView();
  const auto host = view ? view->GetRenderWidgetHost() : nullptr;
  if (!view || !host) {
    callback.Run(gfx::Image());
    return;
  }
  
  const gfx::Size view_size = rect.IsEmpty() ? view->GetViewBounds().size() :
                                               rect.size();
  
  
  
  gfx::Size bitmap_size = view_size;
  const gfx::NativeView native_view = view->GetNativeView();
  const float scale =
      display::Screen::GetScreen()->GetDisplayNearestWindow(native_view)
      .device_scale_factor();
  if (scale > 1.0f)