Summary:
Follow on in https://github.com/facebook/react-native/pull/10864.
**Motivation**
ncuillery Is has a lot of experience with upgrading RN projects (see his [talk](http://www.slideshare.net/ncuillery/introducing-the-new-reactnative-upgrade)) and is rewriting 'react-native upgrade' to use git.
He tells me that we actually want git to merge changes in the .pbxproj file. In his words: "Making the project.pbxproj invisible for "git diff" means that react-native-git-upgrade will never be able to upgrade the project.pbxproj."
Note the git docs explicitly recommend not to use git to merge .pbxproj files: https://git-scm.com/book/en/v2/Customizing-Git-Git-Attributes#Binary-Files
ncuillery do we have an alternative? Some ideas:
1. Use a 3rd-party tool in 'react-native upgrade' to merge the .pbxproj file?
2. We could always re-generate and overwrite the .pbxproj file (never merge) and then run 'react-native link' to update native 3rd-party dependencies in the Xcode project?
3. Last resort: stay away
Closes https://github.com/facebook/react-native/pull/11047
Differential Revision: D4220521
fbshipit-source-id: 823c735856b519be114aa4349ca1392910f00445
3aa25f7917