Should importScripts() detect loops or otherwise abort after too much depth?

[mfalken]

Chrome apparently crashes if sw.js tries to do importScripts(sw.js): https://crbug.com/1180572

This was previously discussed a little at #1041 (comment).

Should importScripts() do something more intelligent than crashing.

@jakearchibald suggested that iframes may have a protection against nesting iframes of the same URL, that we can learn from. cc @wanderview

[wanderview]

This should be easier than the iframe case. Iframes load asynchronously, but importScripts() is synchronous. So we can keep a stack of currently loading scripts and just check if the current script is already loading once already. If so, throw an exception as a loop was detected.