* 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.cc
web_contents()->StopFinding(action);
}
void WebContents::ShowDefinitionForSelection() {
#if defined(OS_MACOSX)
  const auto view = web_contents()->GetRenderWidgetHostView();
  if (view)
    view->ShowDefinitionForSelection();
#endif
}
void WebContents::CopyImageAt(int x, int y) {
  const auto host = web_contents()->GetMainFrame();
  if (host)
    host->CopyImageAt(x, y);
}
void WebContents::Focus() {
  web_contents()->Focus();
}
#if !defined(OS_MACOSX)
bool WebContents::IsFocused() const {
  auto view = web_contents()->GetRenderWidgetHostView();
  if (!view) return false;
  if (GetType() != BACKGROUND_PAGE) {
    auto window = web_contents()->GetNativeView()->GetToplevelWindow();
    if (window && !window->IsVisible())
      return false;
  }
  return view->HasFocus();
}
#endif
void WebContents::TabTraverse(bool reverse) {