how heuristic work? any document?

Unable to reproduce the issue in Win-10 and MacBook Pro (Retina, 15-inch, Mid 2014), 10.12.6 using chrome reported version #61.0.3163.100 and latest canary #64.0.3241.0.

Following are the steps followed to reproduce the issue.
------------
1. opened https://en.wikipedia.org/wiki/IMG_(company) in chrome
2. checked inspector network tab, filtered out img belonging to https://upload.wikimedia.org
3. refreshed tab
4. Observed that in the header's section there was response with cache-control and validated img by sending a request with etag to server as expected.

Attaching screen cast for reference.

denghongcai@ - Could you please verify the screen cast and please let us know if any thing missed from our side. Also please check the issue on latest canary #64.0.3241.0 by creating a new profile without any apps and extensions and please let us know if the issue still persist or not.

Thanks...!!

Deleted: 773990.mp4 2.7 MB

	773990.mp4 2.7 MB View Download

the image whose name starts with 45px

from your captured screen video, it reads from cache without cache-control

Thank you for providing more feedback. Adding requester "krajshree@chromium.org" to the cc list and removing "Needs-Feedback" label.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

This resource in the screenshot in #0 has a large age. In the absence of any explicit lifetime indicator, it looks like the UA is well within the requirements for assuming the resource is fresh based on the freshness_lifetime heuristic.

The presence of the Etag itself doesn't mandate revalidation.

I'll add the cache folks who might have a more definitive answer.

Could someone from Internals>Network>Cache team please take a look into this issue.
Thanks..!

To be more explicit about the heuristic, it uses 10% of time between now and last-modified if that is available, and the response code is appropriate for that (which includes 200) which is the heuristic suggested in section 4.2.2 of RFC 7234:
https://tools.ietf.org/html/rfc7234#section-4.2.2

"   If the response has a Last-Modified header field (Section 2.2 of
   [RFC7232]), caches are encouraged to use a heuristic expiration value
   that is no more than some fraction of the interval since that time.
   A typical setting of this fraction might be 10%.
"

If you always want the resource to be revalidated, please consider something like must-revalidate or max-age=0.

Closing issue since the current behavior is compliant.