Mac: Chrome has finally been optimised for 64-bit Macs in version 39, which comes with lots of stability, performance and security improvements.
Unlike the Windows version, Chrome is now only available in a 64-bit version on the Mac -- so you don't need to install anything new. Just update Chrome to version 39 (previously availbale in beta, now available in the stable channel) and you'll be able to reap the 64-bit benefits.
For more details on the latest update, check out Google's blog post below.
Stable Channel Update [Chrome Releases]