I'm currently using source tarball to build libchromiumcontent[1], which builds by patching a specific stable release of Chromium. The purpose of using source tarball is to make building easier, using gclient to download code takes too much time and it is hard to write an automatic script to wrap around gclient and take care of patching, especially after the migration to git.
I have set up a repo[2] to generate source tarball for all platforms automatically, it works by using fetch --nohooks chromium --target_os=mac,win,linux for bootstrapping and it works fine.
Cheng