oobe: Fix reverse focus for screens with webview parts

Screens with loaded webview parts need focus adjustment after returning
focus from the system tray. But it breaks logic when tab is returned in
reverse order and we need to focus other parts of the screen. This CL
fixes such tab transitions.

Bug: 1133249
Change-Id: I6b565411687e654547935e425272e8f14f1ebaa6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2532576
Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Commit-Queue: Danila Kuzmin <dkuzmin@google.com>
Cr-Commit-Position: refs/heads/master@{#829202}