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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/atom_access_token_store.cc
#include "atom/browser/atom_access_token_store.h"
#include <string>
#include <utility>
#include "atom/browser/atom_browser_context.h"
#include "atom/common/google_api_key.h"
#include "base/environment.h"
#include "content/public/browser/browser_thread.h"
#include "device/geolocation/geolocation_provider.h"
using content::BrowserThread;
namespace atom {
namespace internal {
class TokenLoadingJob : public base::RefCountedThreadSafe<TokenLoadingJob> {
 public:
  explicit TokenLoadingJob(
      const device::AccessTokenStore::LoadAccessTokensCallback& callback)
      : callback_(callback), request_context_getter_(nullptr) {}
  void Run(AtomBrowserContext* browser_context) {