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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
int32_t level,
                                         const base::string16& message,
                                         int32_t line_no,
                                         const base::string16& source_id) {
  if (type_ == BROWSER_WINDOW || type_ == OFF_SCREEN) {
    return false;
  } else {
    Emit("console-message", level, message, line_no, source_id);
    return true;
  }
}
void WebContents::OnCreateWindow(
    const GURL& target_url,
    const std::string& frame_name,
    WindowOpenDisposition disposition,
    const std::vector<std::string>& features,
    const scoped_refptr<content::ResourceRequestBodyImpl>& body) {
  if (type_ == BROWSER_WINDOW || type_ == OFF_SCREEN)
    Emit("-new-window", target_url, frame_name, disposition, features, body);
  else
    Emit("new-window", target_url, frame_name, disposition, features);
}
void WebContents::WebContentsCreated(content::WebContents* source_contents,