Skin the Challenges frame's Gamemodes tab

The Trials shape a third time, and again suffix for suffix: the search
box and list container are named off the tab exactly as Trials names
its own, the list's only region is the same store divider, and the
scroll arrows hang off the scroll frame rather than off the bar. So the
divider constant is shared rather than copied and the three calls go in
unchanged.

The one difference is the filter, which this tab does not have. Its two
children are the search box and the list and neither is a menu, so
there is nothing for a Dropdown call to be handed. That is written into
the comment rather than left implicit: with the same function sitting
three times over in the file, a missing fourth line otherwise reads as
an oversight.

The tab owns no regions of its own at all, so nothing here needs the
keepTextures care the Rewards tab's PageText took. Both children exist
on a cold reload, before the tab has ever been opened, and the counts
are unchanged after a click, so it rides SkinContents with the rest
rather than needing a hook on its own OnShow.

Everything reuses an existing helper, so the shared layer is unchanged.

Modules/ChallengesFrame.lua

@@ -129,8 +129,8 @@ local function UpdatePanelTop(frame)
 end
 
 -- Per-tab contents. Each of the six tabs owns its own copy of these widgets
--- rather than sharing one set, so they're skinned per tab; Trials, Rewards and
--- Challenges are done and the rest follow the same shape.
+-- rather than sharing one set, so they're skinned per tab; Trials, Rewards,
+-- Challenges and Gamemodes are done, and the two left follow the same shape.
 --
 -- Nothing about one tab's naming carries to the next: the Trials search box is
 -- "...TrialsTabSearch" and its filter a "...FilterDropDown", where the Rewards
@@ -336,6 +336,37 @@ local function SkinChallengesTab()
 	)
 end
 
+local GAMEMODES_TAB = FRAME_NAME.."GamemodesTab"
+local GAMEMODES_LIST = GAMEMODES_TAB.."Challenges"
+local GAMEMODES_SCROLL = GAMEMODES_LIST.."ScrollFrame"
+
+-- The Trials/Challenges shape a third time, and again suffix for suffix: the
+-- same search box and list names, the same store divider as its list
+-- container's only region, the same arrows named off the scroll frame rather
+-- than off the bar (probed). See SkinTrialsTab above for why each call is the
+-- call it is.
+--
+-- What differs is the filter: there isn't one, and that's the tab's own shape
+-- rather than something missed here. It has exactly two children, the search
+-- box and the list, and neither of them is a menu (probed), so there is nothing
+-- for a Skin:Dropdown line to be handed.
+--
+-- It owns no regions of its own either (probed), so nothing here needs the
+-- keepTextures care the Rewards tab's PageText took. And everything under it
+-- exists before the tab has ever been opened -- two children and no regions on
+-- a cold reload, unchanged after a click -- so it rides SkinContents like the
+-- other three rather than needing a hook on the tab's own OnShow.
+local function SkinGamemodesTab()
+	Skin:SearchBox(_G[GAMEMODES_TAB.."Search"])
+	Skin:StripArtByFile(_G[GAMEMODES_LIST], LIST_DIVIDER_ART)
+	Skin:ScrollBar(
+		_G[GAMEMODES_SCROLL.."ScrollBar"],
+		_G[GAMEMODES_SCROLL.."ScrollBarThumb"],
+		_G[GAMEMODES_SCROLL.."ScrollUpButton"],
+		_G[GAMEMODES_SCROLL.."ScrollDownButton"]
+	)
+end
+
 -- The close button is anchored inside the frame's own top-right corner, which
 -- stopped being the corner the player sees once the panel grew up over the title
 -- band -- it ends up floating a title's height below the top edge. Re-anchored
@@ -367,6 +398,7 @@ local function SkinContents()
 	AnchorTabRow()
 	SkinTrialsTab()
 	SkinStoreTab()
+	SkinGamemodesTab()
 	SkinChallengesTab()
 end