cache race helper functions

[zerotacg]

Hi,
I just wanted to share some minimal helper functions [1] that makes the "cache races against network with potential dual rendering" a little easier by having the cache reject if the network fullfills [2] and have the network reject only if the cache also rejects [3]

[1] https://gist.github.com/zerotacg/d304348cdd5d2f965901
[2] https://gist.github.com/zerotacg/d304348cdd5d2f965901#file-network-cache-race-js-L21
[3] https://gist.github.com/zerotacg/d304348cdd5d2f965901#file-network-cache-race-js-L12