Enable Stale While Revalidate support by default.

Approved intent to ship:
https://groups.google.com/a/chromium.org/d/msg/blink-dev/rspPrQHfFkI/rrhGyO4DBwAJ

BUG=348877

Change-Id: I5f2931283ff5c86a063573b4742379ea5eee1d95
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1521570
Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#640745}
1 file changed