Make ServiceWorkerFetchRequest and ServiceWorkerResponse header maps case insensitive
When storing headers in a map the map should be case insensitive (like HTTPHeaderMap in Blink) so that headers can be easily searched for and coalesced when necessary.
BUG=
392621
Committed:
https://crrev.com/f96d19ba7ea5be53ece63b9f6da963aaba2039c2
Cr-Commit-Position: refs/heads/master@{#296387}