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Do not cache a page if the main resource of its main document had
cache-control: no-store header.

Note that it's the only set of conditions that disabled bfcache.
Back-forward cache is still enabled in the following scenarios:
- no-cache directive
- no-store on a non-main resource (e.g. image)
- no-store on a main resource of a subframe.

This matches Safari's implementation of back-forward cache:
https://bugs.webkit.org/show_bug.cgi?id=140302

R=arthursonzogni@chromium.org,lowell@chromium.org
BUG=1014925

Change-Id: Ie1185462dc0420dc2a4b1b16f93b22a649bb67ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1865337
Commit-Queue: Alexander Timin <altimin@chromium.org>
Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707207}