In this situation a while loop needs to make an unnecessary check at the begining. This loop is designed to make at least one iteration. In this case a better option is to use do-while. And it is also a good practice not to make such code.
Created attachment 218047 [details] patch
For the simple boolean test, I doubt this has much benefit. Did you do some profiling that showed this as a hotspot? I think your code is probably more correct, but I'm not sure it's worth changing at this point.
Comment on attachment 218047 [details] patch Clearing flags on attachment: 218047 Committed r184073: <http://trac.webkit.org/changeset/184073>
All reviewed patches have been landed. Closing bug.