Extension for Chrome that redirects you to an existing tab if you try and open the same url
EDIT Previously linked extension doesn't work. Only One, however appears to work flawlessly.
This should do the trick for you, though the logic is a bit differet in that it closes the OLD tab and opens the NEW tab. Same effect in the end though.
Fast Unique Tab is what you're looking for.
The other extensions mentioned here are vastly outdated and some simply don't work.
Based on review here -
Duplicate Tab - Simple, effective and fast
Clutter Free - Same with Whitelisting option. #recommended
Unique Tabs - Only notification, no redirection