* 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
const MediaPlayerId& id) {
  Emit("media-paused");
}
void WebContents::DidChangeThemeColor(SkColor theme_color) {
  Emit("did-change-theme-color", atom::ToRGBHex(theme_color));
}
void WebContents::DocumentLoadedInFrame(
    content::RenderFrameHost* render_frame_host) {
  if (!render_frame_host->GetParent())
    Emit("dom-ready");
}
void WebContents::DidFinishLoad(content::RenderFrameHost* render_frame_host,
                                const GURL& validated_url) {
  bool is_main_frame = !render_frame_host->GetParent();
  Emit("did-frame-finish-load", is_main_frame);
  if (is_main_frame)
    Emit("did-finish-load");
}
void WebContents::DidFailLoad(content::RenderFrameHost* render_frame_host,
                              const GURL& url,
                              int error_code,
                              const base::string16& error_description,
                              bool was_ignored_by_handler) {
  bool is_main_frame = !render_frame_host->GetParent();
  Emit("did-fail-load", error_code, error_description, url, is_main_frame);
}
void WebContents::DidStartLoading() {