Add shivanisha@chromium.org to OWNERS for //net/http/http_cache_*

Bug: 
Change-Id: Iab20bd4453111727924d9eb7de040e6a48c13909
Reviewed-on: https://chromium-review.googlesource.com/811825Reviewed-by: Shivani Sharma <shivanisha@chromium.org>
Commit-Queue: Julia Tuttle <juliatuttle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522177}

net/disk_cache/OWNERS

-morlovich@chromium.org
 jkarlin@chromium.org
+morlovich@chromium.org
 
 # COMPONENT: Internals>Network>Cache

net/http/OWNERS

+per-file http_cache_*=shivanisha@chromium.org
 per-file transport_security_state_static.*=elawrence@chromium.org
-per-file transport_security_state_static.*=palmer@chromium.org
\ No newline at end of file
+per-file transport_security_state_static.*=palmer@chromium.org