Reland "[TabStripComboButton] Fix TabStripRegionViewBrowserTest class."

This is a reland of commit 7f71ccb7f703b62ee184cebb7b8fbda84a13fade

Removed unused variable is_right_aligned_

Original change's description:
> [TabStripComboButton] Fix TabStripRegionViewBrowserTest class.
>
> This CL adds coverage for TabStripRegionViewBrowserTest for combobutton feature to ensure field trial config works. This parametrizes the test to run with and without the combobutton.
>
> With the combo-button the tab search should exist after the last tab instead of start and end of the tabstrip irrespective of tabs::kTabSearchPositionSetting.
>
> Additionally, tabs::GetTabSearchTrailingTabstrip() should not be applicable with combobutton as the tab search will always exist after the last tab.
>
> Bug: 384569726
> Change-Id: I55fefd1ce28dcfa3472d5a802ae88ce7a964610e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6098171
> Reviewed-by: Emily Shack <emshack@chromium.org>
> Commit-Queue: Shibalik Mohapatra <shibalik@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1397438}

Bug: 384569726
Change-Id: I5349e34dd00fa7d3528de16002b2cc2587c662e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6106858
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Shibalik Mohapatra <shibalik@chromium.org>
Reviewed-by: Emily Shack <emshack@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1398307}