Summary: I found that if you move a subview to a different index, it would cause a crash in subsequent layout passes because the `CSSNodeRef` representing it was being re-inserted into the list. I spent a lot of time figuring out the best way to "diff" the view hierarchy from before and after, and I found the easiest implementation is also the most reliable. We can continue to optimize, but this is a great start.
Reviewed By: emilsjolander
Differential Revision: D4218623
fbshipit-source-id: 06253089492ac37ae4b94b7c30140ce6ed680ed2
dc10fdd958