<!--
Thanks for opening an issue! A few things to keep in mind:

- The issue tracker is only for bugs and feature requests.
- Before reporting a bug, please try reproducing your issue against
  the latest version of Electron.
- If you need general advice, join our Slack: http://atom-slack.herokuapp.com
-->

* 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
const gfx::Rect& pos) {
  Emit("move", pos);
}
void WebContents::CloseContents(content::WebContents* source) {
  Emit("close");
  if ((type_ == BROWSER_WINDOW || type_ == OFF_SCREEN) && owner_window())
    owner_window()->CloseContents(source);
}
void WebContents::ActivateContents(content::WebContents* source) {
  Emit("activate");
}
void WebContents::UpdateTargetURL(content::WebContents* source,
                                  const GURL& url) {
  Emit("update-target-url", url);
}
bool WebContents::IsPopupOrPanel(const content::WebContents* source) const {
  return type_ == BROWSER_WINDOW;
}
void WebContents::HandleKeyboardEvent(
    content::WebContents* source,
    const content::NativeWebKeyboardEvent& event) {
  if (type_ == WEB_VIEW && embedder_) {
    
    embedder_->HandleKeyboardEvent(source, event);
  } else {
    
    CommonWebContentsDelegate::HandleKeyboardEvent(source, event);
  }
}
bool WebContents::PreHandleKeyboardEvent(