* Add optional horizontal tab strip scroll buttons
Introduce a profile preference (Appearance → Tabs) to show leading and
trailing scroll controls when the horizontal unpinned tab area overflows.
Expose the pref through settings WebUI, extension settings_private, and the
incognito allowlist where appropriate.
BraveHorizontalTabStripRegionView inserts TabStripControlButton instances
with flex-friendly child ordering and visibility tied to overflow. Scroll
offset changes are observed via BraveTabContainer’s
RegisterHorizontalScrollOffsetChangedCallback subscription.
Sangwoo Ko
21ca687cb4