commit c02e3852530f690b7a6645708d5fa0eb992d2685
author Mark Cogan <marq@google.com> Tue Aug 03 17:07:00 2021
committer Chromium LUCI CQ <chromium-scoped@luci-project-accounts.iam.gserviceaccount.com> Tue Aug 03 17:07:00 2021
tree 9a3296ccbcc973e1e85c021d45ad1308f71a5eba
parent 75ec0dc8b955ebc2b2152395d362a8d330d54ce2

[iOS] Remove TabModel

This CL factors out the remaining responsibilities of TabModel and
removes it. It introduces a functional change in how sessions are saved
when scenes background.

For the purposes of this code, "saving sessions" involves both updating
the session store and writing out snapshots of the active web states.

TabModels -- which were per-browser objects -- listed for the
UIApplication lifecycle notifications to determine when to save
sessions. This means that when the application backgrounds, all of the
connected scenes save the sessions for the active webstates in their
browsers. It also means that sessions are *not* saved when individual
scenes background. (This is not the only trigger for saving sessions
in Chrome, just the one determined by app/scene lifecycles).

This CL changes this backgrounding logic, moving it to a scene state
agent. This agent observes the scene state transitions, and now it
saves sessions per-scene, whenever that scene backgrounds.

The other responsibility of TabModel was to close all of the web states
in a web state list when the owning Browser is shut down. This CL moves
that responsibility to BrowserViewWrangler, which is the current owner
of Browser lifecycles. Potentially it could be migrated to the
BrowserImpl class in the future for even better encapsulation.

Because there are some circumstances where the app may shut down
without being backgrounded (if it is force-quit in the app switcher
when no other apps are present, for example), this CL adds a check to
the shutdown code in SceneController that asks the scene to save the
session if needed. (Sessions are marked as needing saving if the
scene has foregrounded since the previous save).

Bug: 1045575, 1115611, 1110966, 783777
Change-Id: Ic70f4d1b839ab95757196a805ccac21c36b7dc83
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3063619
Commit-Queue: Mark Cogan <marq@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Mohammad Refaat <mrefaat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#908028}