In this particular case, they were not optimizing for Chrome. They generated the code that was obvious to generate. Because of a perf bug in WebKit they added

In this particular case, they were not optimizing for Chrome. They generated the code that was obvious to generate. Because of a perf bug in WebKit they added a flag to generate less correct code that is fast in WebKit. If anything, it's a case of optimizing towards WebKit. But really, it's a case of performance bug in WebKit and them adding a work-around.