[Dridzt]

I have a feeling this snippet is redundant (not related to the original enquiry)

if (frame:GetScript("OnShow")) then
  frame:HookScript("OnShow", hideTab)
else
  frame:SetScript("OnShow", hideTab)
end

:HookScript() should function as :SetScript() automatically if the handler doesn't exist.

So the whole control structure could be simplified to just:

if frame and not frame.tabHooked then
  frame:HookScript("OnShow", hideTab)
  frame.tabHide = true
  frame.tabHooked = true
  frame:Hide()
end

Edit: Also where is the shown variable defined / gets its value? (used in GetNumActiveChatFrames() function)