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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.h
content::NavigationHandle* navigation_handle) override;
  void DidFinishNavigation(
      content::NavigationHandle* navigation_handle) override;
  bool OnMessageReceived(const IPC::Message& message) override;
  void WebContentsDestroyed() override;
  void NavigationEntryCommitted(
      const content::LoadCommittedDetails& load_details) override;
  void TitleWasSet(content::NavigationEntry* entry, bool explicit_set) override;
  void DidUpdateFaviconURL(
      const std::vector<content::FaviconURL>& urls) override;
  void PluginCrashed(const base::FilePath& plugin_path,
                     base::ProcessId plugin_pid) override;
  void MediaStartedPlaying(const MediaPlayerInfo& video_type,
                           const MediaPlayerId& id) override;
  void MediaStoppedPlaying(const MediaPlayerInfo& video_type,
                           const MediaPlayerId& id) override;
  void DidChangeThemeColor(SkColor theme_color) override;
  
  void Observe(int type,
               const content::NotificationSource& source,
               const content::NotificationDetails& details) override;
  
  void DevToolsReloadPage() override;
  
  void DevToolsFocused() override;
  void DevToolsOpened() override;
  void DevToolsClosed() override;
 private:
  struct LoadURLParams {
    LoadURLParams() : params(GURL()), id(0) {}