Calculate prefetched value

Calculate the prefetched value as opposed to a prefetchType

`spfPrefetch` contains the boolean value of whether the request was a prefetch or not.

`spfPrefetch && !spfCached` implies the request was a promote
`spfPrefetch && spfCached` implies a prefetch cache hit
Can you confirm that the compiler will obfuscate this `cached.response` reference the same as `cacheValue.response` below in `setCacheObject_`?  (You might need to create a typedef and typecast, but I'm not sure.)