https://codereview.chromium.org/1854643002/

Important things to consider:
* When in foreground, the offlining prerender should not compete with other prerenders
* It would be nice to get offlining prerenders killed as soon as Chrome is foregrounded, this should be the responsibility of the caller, I think
* On low end devices the offlining prerender should be allowed, but it should not spawn new renderers if one background renderer process (from a tab) is already alive

talo, dimich, dougarnett: Under Settings->Privacy there is "Use prediction service to load pages more quickly". We normally get prerenders disabled if the user chooses to opt out there.

If I understand correctly, we want to ignore this setting when background offliner asks the PrerenderManager to AddPrerenderForOffline().

Yes, that would be my take too. I think we would want to make a policy decision at higher level on whether to do prerenders for an user-directed async load request vs. maybe not for speculative requests.

+1, our first feature using the prerenderer will be Async Loading which will be a very explicit user action every time, and not a speed optimization, so this check is not directly applicable.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fde8d42d16c0fac930e7fe39e86cb3ef6d24e9c8

commit fde8d42d16c0fac930e7fe39e86cb3ef6d24e9c8
Author: gabadie <gabadie@chromium.org>
Date: Thu Apr 28 14:17:51 2016

Implement PrerenderManager::AddPrerenderForOffline()

Offline's operation of fetching and snapshoting a web page
is going to be experienced with Prerender. This CL add the
offline Prerender origin in that purpose with the
PrerenderManager::AddPrerenderForOffline() method.

BUG= 599500 

Review-Url: https://codereview.chromium.org/1854643002
Cr-Commit-Position: refs/heads/master@{#390370}

[modify] https://crrev.com/fde8d42d16c0fac930e7fe39e86cb3ef6d24e9c8/chrome/browser/prerender/prerender_histograms.cc
[modify] https://crrev.com/fde8d42d16c0fac930e7fe39e86cb3ef6d24e9c8/chrome/browser/prerender/prerender_manager.cc
[modify] https://crrev.com/fde8d42d16c0fac930e7fe39e86cb3ef6d24e9c8/chrome/browser/prerender/prerender_manager.h
[modify] https://crrev.com/fde8d42d16c0fac930e7fe39e86cb3ef6d24e9c8/chrome/browser/prerender/prerender_origin.cc
[modify] https://crrev.com/fde8d42d16c0fac930e7fe39e86cb3ef6d24e9c8/chrome/browser/prerender/prerender_origin.h
[modify] https://crrev.com/fde8d42d16c0fac930e7fe39e86cb3ef6d24e9c8/chrome/browser/prerender/prerender_unittest.cc
[modify] https://crrev.com/fde8d42d16c0fac930e7fe39e86cb3ef6d24e9c8/tools/metrics/histograms/histograms.xml