ResourceHandlerImpl.handleResourceRequest takes too long to deliver a 304. From
my point of view, delivering a 304 should take quasi no time.
The problem seems to be that ResourceManager.findLibrary is called again and
again. Can resources really change in production mode?
If resources can't change in production mode, simply cache all necessary
information (most notably last modified) and return 304 immediately.
I will look deeper into this. Maybe i will find some point to change.