So you are saying that e.g. a 3 month old tab should not appear in the recent tab section. Right?
Do you know how long we keep open tabs in the cache? Until they get closed (=indefinitely) or is there some TTL attached to each entry in the cache?

> So you are saying that e.g. a 3 month old tab should not appear 
> in the recent tab section. Right?

I am not saying this. I was talking about implementation detail, which I need to change.

> Do you know how long we keep open tabs in the cache?
If you mean when Last1 offline pages are removed, then the aim is to remove them when the tab is closed. Current they are removed once in a while.

CL https://codereview.chromium.org/2595873002

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ad80f041ddc7bff1360592184661fd51bdf414e9

commit ad80f041ddc7bff1360592184661fd51bdf414e9
Author: vitaliii <vitaliii@chromium.org>
Date: Wed Dec 21 14:41:08 2016

[NTP::RecentTabs] Do not fetch all pages when not a recent tab is added.

Currently, all offline pages are fetched when a new offline page is
added (even it if is not a recent tab). However, there is no sense to
refetch if there is no new recent tabs.

This CL changes the logic to fetch only when the added offline page is a
recent tab.

BUG= 672433 

Review-Url: https://codereview.chromium.org/2595873002
Cr-Commit-Position: refs/heads/master@{#440096}

[modify] https://crrev.com/ad80f041ddc7bff1360592184661fd51bdf414e9/components/ntp_snippets/offline_pages/recent_tab_suggestions_provider.cc
[modify] https://crrev.com/ad80f041ddc7bff1360592184661fd51bdf414e9/components/ntp_snippets/offline_pages/recent_tab_suggestions_provider_unittest.cc