R1:a4053bb5808e

When a ChangesetList sleeps after a Quicksand navigation, also hide any visible banner

Summary: Fixes T13080. The banner wasn't properly included in the sleep/wake logic.

Test Plan:
Mentioned `Dxxx` on a task. Enabled persistent chat to activate Quicksand. Reloaded page. Clicked `Dxxx`. Scrolled down until a changeset header appeared. Pressed back button.

- Before patch: ended up on task, with header still around.
- After patch: ended up on task, with header properly vanquished.

Pressed "forward"…