0. Ideally one could use widely used tools to sync and build webkit. (This requirement is simply about making things simple and reliable.)
1. I would like to be able to switch branches in git and be able to build.
2. I would not like my sync time to increase dramatically. (Based on various measurements, gyp generation may add between 5% to 40% overhead to a sync -- although the gyp generation time is consistent, the sync time varies)
3. I have a concern that having gyp generation happen on a developers machine after sync'ing may not work due to a slightly different machine configuration or a badly tested change in the gyp generation tool, etc.
Now there is a concern that one could do a gyp change and not check in the generated files but we could have a test that runs to verify that the checked in version matches the generated version.