[whatwg] Structured clone algorithm on LocalStorage

[João Eiras]

> and the more browser UI jank users will be sure to experience.

If I may, as a side note, locking the UI is a user agent specific issue.  
No specification requires user agents to lock their UIs while scripts  
execute.
Opera has achieved this long time ago, by properly dividing ecmascript  
execution with all the other tasks, and the new browsers with  
multi-process architecture also do not suffer from this problem.