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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
#include "atom/browser/api/atom_api_web_contents.h"
#include <set>
#include <string>
#include "atom/browser/api/atom_api_debugger.h"
#include "atom/browser/api/atom_api_session.h"
#include "atom/browser/api/atom_api_window.h"
#include "atom/browser/atom_browser_client.h"
#include "atom/browser/atom_browser_context.h"
#include "atom/browser/atom_browser_main_parts.h"
#include "atom/browser/lib/bluetooth_chooser.h"
#include "atom/browser/native_window.h"
#include "atom/browser/net/atom_network_delegate.h"
#include "atom/browser/osr/osr_output_device.h"
#include "atom/browser/osr/osr_render_widget_host_view.h"
#include "atom/browser/osr/osr_web_contents_view.h"
#include "atom/browser/ui/drag_util.h"
#include "atom/browser/web_contents_permission_helper.h"
#include "atom/browser/web_contents_preferences.h"
#include "atom/browser/web_contents_zoom_controller.h"
#include "atom/browser/web_view_guest_delegate.h"
#include "atom/common/api/api_messages.h"
#include "atom/common/api/event_emitter_caller.h"
#include "atom/common/color_util.h"
#include "atom/common/mouse_util.h"
#include "atom/common/native_mate_converters/blink_converter.h"
#include "atom/common/native_mate_converters/callback.h"