Here’s a handy command for the Terminal that will get and unzip the latest Mac Chrome Nightly build:
curl -O http://build.chromium.org/buildbot/snapshots/chromium-rel-mac/`curl http://build.chromium.org/buildbot/snapshots/chromium-rel-mac/LATEST`/chrome-mac.zip;unzip chrome-mac.zip;rm chrome-mac.zip

If you have issues with it re-requesting keychain stuff, you can sign the chrome app and the helper app using codesign with your own codesigning identity and it won’t ask again, I use this:
find chrome-mac/. -name \*.app -exec codesign -s ‘Tom Hennigan’ ‘{}’ \;