Make sure our cache isolation works with cache2

Mozilla wrote a new cache back-end which landed in the 32 release cycle and has a bunch of new features like

The new HTTP cache back end has many improvements like request prioritization optimized for first-paint time, ahead of read data preloading to speed up large content load, delayed writes to not block first paint time, pool of most recently used response headers to allow 0ms decisions on reuse or re-validation of a cached payload, 0ms miss-time look-up via an index, smarter eviction policies using frecency algorithm

(http://www.janbambas.cz/new-firefox-http-cache-enabled/)

We should make sure that our cache isolation patches get properly rewritten and no new information leaks occur.

See: https://bugzilla.mozilla.org/show_bug.cgi?id=913806 and https://developer.mozilla.org/en-US/docs/HTTP_Cache for further information.