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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/common_web_contents_delegate.h
class AtomJavaScriptDialogManager;
class NativeWindow;
class WebDialogHelper;
class CommonWebContentsDelegate
    : public content::WebContentsDelegate,
      public brightray::InspectableWebContentsDelegate,
      public brightray::InspectableWebContentsViewDelegate {
 public:
  CommonWebContentsDelegate();
  virtual ~CommonWebContentsDelegate();
  
  
  void InitWithWebContents(content::WebContents* web_contents,
                           AtomBrowserContext* browser_context);
  
  void SetOwnerWindow(NativeWindow* owner_window);
  void SetOwnerWindow(content::WebContents* web_contents,
                      NativeWindow* owner_window);
  
  void DestroyWebContents();
  
  content::WebContents* GetWebContents() const;
  
  content::WebContents* GetDevToolsWebContents() const;
  brightray::InspectableWebContents* managed_web_contents() const {