This is a bit of a construed case, but it's completely reproducible.

- Outside VR, ensure that only one tab is open, an incognito tab.
- Enter VR, then use the overflow menu to close that one tab.
- You'll be brought to a black content quad, which itself isn't good, but not the subject of the bug here.
- Hover on the black content, and scroll.  You'll immediately crash the browser with:

signal 6 (SIGABRT), code -6 (SI_TKILL), fault addr --------
[FATAL:ui_input_manager.cc(199)] Check failed: gesture_list->front()->GetType() == blink::WebInputEvent::kGestureScrollEnd (15 vs. 12)

It is possible we should never get to this state, if we force the new tab page to spawn when all tabs are otherwise close.