Cros: Initialize HotseatState

This was causing an msan failure (use of uninitialized var).

Bug: 1003006
Change-Id: Iad05067b34e8289ce0809d6bc2ce935b58f0397b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1797060
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Reviewed-by: Manu Cornet <manucornet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695747}

ash/shelf/shelf_layout_manager.cc

@@ -233,6 +233,7 @@ ShelfLayoutManager::State::State()
     : visibility_state(SHELF_VISIBLE),
       auto_hide_state(SHELF_AUTO_HIDE_HIDDEN),
       window_state(WorkspaceWindowState::kDefault),
+      hotseat_state(HotseatState::kShown),
       pre_lock_screen_animation_active(false),
       session_state(session_manager::SessionState::UNKNOWN) {}