Add load flags and response bits to communicate Stale While Revalidate.

This change does not implement anything other than plumbing load
and response bits from the network stack across from the blink
loader.

BUG=348877

Change-Id: Id2b455352b8b26c93cf5e87bee054db90e774480
Reviewed-on: https://chromium-review.googlesource.com/1101237
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567722}
16 files changed