1) Forking in open source is not a crime, it is a virtue and fundamental right
2) By "after what Google did with Chrome", do you mean contributing massive amounts of engineering resources to WebKit for several years, exceeding Apple's own WebKit team? Look here: http://www.kaizou.org/2013/04/why-google-dropped-webkit/
If someone's forking your project, it's usually because productivity/velocity is going down because of either too much political contention, or too much legacy code.
I've never seen any indication that Apple valued their "market share" from Chrome using WebKit in any way, and the people actually working on WebKit for Apple were mostly happy about the fork.
2) By "after what Google did with Chrome", do you mean contributing massive amounts of engineering resources to WebKit for several years, exceeding Apple's own WebKit team? Look here: http://www.kaizou.org/2013/04/why-google-dropped-webkit/
If someone's forking your project, it's usually because productivity/velocity is going down because of either too much political contention, or too much legacy code.