Here is a link to the wiki page describing how to use git with webkit:
http://trac.webkit.org/wiki/UsingGitWithWebKit
There is really nothing fancy to do, since we are not committers on webkit. Simply:
git clonegit://git.webkit.org/WebKit.git WebKit
Each revision in svn corresponds to a different commit in git. In bonus the whole repository in git is 1.7 GB compared to 2.0 GB for the latest revision checkout of the svn repo!
Erick