When in-memory cached resources are requested using
If-Modified-Since HTTP header, we can then safely
return a 304 without having to transfer the entire
payload over the network.
This change completes the fix [1]: now that we have
the lastModified date into the SmallResource object
we can use it to actually save bandwidth and allow
better client response time.
[1] https://gerrit-review.googlesource.com/#/c/57213/
Change-Id: If268acacc167a2062260008a3b9767e055970d43
c06b6c4615