* 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 mate::Dictionary& options);
  
  bool DidAddMessageToConsole(content::WebContents* source,
                              int32_t level,
                              const base::string16& message,
                              int32_t line_no,
                              const base::string16& source_id) override;
  void WebContentsCreated(content::WebContents* source_contents,
                          int opener_render_process_id,
                          int opener_render_frame_id,
                          const std::string& frame_name,
                          const GURL& target_url,
                          content::WebContents* new_contents) override;
  void AddNewContents(content::WebContents* source,
                      content::WebContents* new_contents,
                      WindowOpenDisposition disposition,
                      const gfx::Rect& initial_rect,
                      bool user_gesture,
                      bool* was_blocked) override;
  content::WebContents* OpenURLFromTab(
      content::WebContents* source,
      const content::OpenURLParams& params) override;
  void BeforeUnloadFired(content::WebContents* tab,
                         bool proceed,
                         bool* proceed_to_fire_unload) override;
  void MoveContents(content::WebContents* source,
                    const gfx::Rect& pos) override;
  void CloseContents(content::WebContents* source) override;