[kevingadd]

It's unfortunate that Chrome's definition of 'mandatory' is flexible in a bad way. If you've done enough performance profiling of webapps in Chrome you may have noticed that even cached resources can take over 20ms to load from cache - this is because all cache loads have to go between processes, so they get delayed until thread/process switches can happen and messages can get ferried back and forth. If you're unlucky, you eat this delay on every resource you load. In some cases this can add over a second to load time for an application.

You might think 'well this calls for prefetch, right? load them all at once'. You're right! Except it doesn't work. Chrome content processes ignore prefetch directives, all they seem to do is ensure that they're in cache - so there's no way to avoid eating this 20+ms hit per-resource.

Ideally you control all the code being run in your app so you can just issue the relevant XHR requests to load everything up-front and not block on those requests, but I've frequently run into cases where a downloaded resource loads other resources, etc. Really frustrating that caching and prefetch are so slow in Chrome and there's no indication that they will fix it.

It's my understanding that in comparison Safari does not have this hit per-asset, loading the applications I've tested is dramatically faster on an iPhone compared to Chrome on a desktop PC. :(