* Electron version: 1.6.3
* Operating system: Linux

### Expected behavior

When registering a `beforeunload` handler which cancels unloading, I would expect the handler to be called for every `BrowserWindow.reload()`.

### Actual behavior

On 1.6.3, the `beforeunload` handler is called for the first `reload` but not on subsequent calls. Even after removing the event handler, `reload` will not reload the window anymore.

### How to reproduce

```javascript
const cancelUnload = e => {
   console.log('cancelUnload called')
   e.returnValue = false
}

window.addEventListener('beforeunload', cancelUnload)

remote.getCurrentWindow().reload()  // [1] -> cancelUnload called
remote.getCurrentWindow().reload()  // [2] -> cancelUnload called

remote.getCurrentWindow().close()   // [3] -> cancelUnload called
remote.getCurrentWindow().close()   // [4] -> cancelUnload called

window.removeEventListener('beforeunload', cancelUnload)

remote.getCurrentWindow().reload()  // [5] -> reloads window

remote.getCurrentWindow().close()   // [6] -> closes window
```
I would expect `cancelUnload` to be printed to the console four times and the step at `[5]` to actually reload the window. This is works up to Electron 1.6.2.

On Electron 1.6.3 `cancelUnload` is not printed at step `[2]` (nor on any subsequent calls to reload). What's more, event after removing the `beforeunload` handler, `reload` does not work anymore: at step `[5]` the window does not reload (but closing the window at `[6]` works).
atom/browser/api/atom_api_web_contents.h
const content::MediaStreamRequest& request,
      const content::MediaResponseCallback& callback) override;
  void RequestToLockMouse(
      content::WebContents* web_contents,
      bool user_gesture,
      bool last_unlocked_by_target) override;
  std::unique_ptr<content::BluetoothChooser> RunBluetoothChooser(
      content::RenderFrameHost* frame,
      const content::BluetoothChooser::EventHandler& handler) override;
  
  void BeforeUnloadFired(const base::TimeTicks& proceed_time) override;
  void RenderViewCreated(content::RenderViewHost*) override;
  void RenderViewDeleted(content::RenderViewHost*) override;
  void RenderProcessGone(base::TerminationStatus status) override;
  void DocumentLoadedInFrame(
      content::RenderFrameHost* render_frame_host) override;
  void DidFinishLoad(content::RenderFrameHost* render_frame_host,
                     const GURL& validated_url) override;
  void DidFailLoad(content::RenderFrameHost* render_frame_host,
                   const GURL& validated_url,
                   int error_code,
                   const base::string16& error_description,
                   bool was_ignored_by_handler) override;
  void DidStartLoading() override;
  void DidStopLoading() override;
  void DidGetResourceResponseStart(
      const content::ResourceRequestDetails& details) override;
  void DidGetRedirectForResourceRequest(
      const content::ResourceRedirectDetails& details) override;
  void DidStartNavigation(