Can I prevent Chrome from storing passwords in Keychain, instead just save it to itself?
Open Chrome then on the right site click on

Click the Chrome menu Chrome menu on the browser toolbar.
Select Settings.
Click Show advanced settings.
Under the "Passwords and forms" section check the "Offer to save your web passwords" checkbox if you want Google Chrome to prompt you to save your password every time you sign in to a new website.

Open your KeyChain and find the Google/Chrome passwords that you do not want to share. Open and select Access control. Now use one of the available options to your desire (to share or not).