Nicely done!
If, like me, you collect a lot of Chrome windows you'll find this slightly faster:
tell application "Google Chrome"
repeat with eachWindow in (get every window)
try
tell (contents of eachWindow)
set theID to id of (item 1 of (get every tab whose URL contains targetText))
repeat with i from 1 to (count of every tab)
if id of tab i = theID then exit repeat
end repeat
set active tab index to i
set index to 1
end tell
return "FOUND"
on error
-- do nothing
end try
end repeat
end tell
return "NOT FOUND"
...because it checks all of the tabs of a window for the URL in one go, then only iterates through a window's tabs if there's going to be a match.
Yours is a very clean and neat solution. If you want some ideas for expanding it, I ripped the above code from a subroutine I posted, which is nowhere as good as @_jims's do-it-all absolute monster.