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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
v8::Locker locker(isolate());
  v8::HandleScope handle_scope(isolate());
  devtools_web_contents_.Reset();
  Emit("devtools-closed");
}
bool WebContents::OnMessageReceived(const IPC::Message& message) {
  bool handled = true;
  IPC_BEGIN_MESSAGE_MAP(WebContents, message)
    IPC_MESSAGE_HANDLER(AtomViewHostMsg_Message, OnRendererMessage)
    IPC_MESSAGE_HANDLER_DELAY_REPLY(AtomViewHostMsg_Message_Sync,
                                    OnRendererMessageSync)
    IPC_MESSAGE_HANDLER_DELAY_REPLY(AtomViewHostMsg_SetTemporaryZoomLevel,
                                    OnSetTemporaryZoomLevel)
    IPC_MESSAGE_HANDLER_DELAY_REPLY(AtomViewHostMsg_GetZoomLevel,
                                    OnGetZoomLevel)
    IPC_MESSAGE_HANDLER_CODE(ViewHostMsg_SetCursor, OnCursorChange,
      handled = false)
    IPC_MESSAGE_UNHANDLED(handled = false)
  IPC_END_MESSAGE_MAP()
  return handled;
}
void WebContents::WebContentsDestroyed() {