Any idea in which Chrome release we can expect this to be available?

Seb, can I hand this off to you to take care of? Basically, we want a feature-flag that disables all "heuristic" protections in CanFreeze/CanDiscard, allowing devs to experiment with lifecycles using a live browser.

Sure, I'll take this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/494dcbfa7da1c0cd848a12212e096e015be0c024

commit 494dcbfa7da1c0cd848a12212e096e015be0c024
Author: Sebastien Marchand <sebmarchand@chromium.org>
Date: Fri Oct 05 16:56:30 2018

Add a feature flag to disable the proactive discarding protections

Bug:  876348 
Change-Id: Ib932652af7814f421009be79a7e9a1e5413fffd7
Reviewed-on: https://chromium-review.googlesource.com/c/1228505
Commit-Queue: Sébastien Marchand <sebmarchand@chromium.org>
Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597171}
[modify] https://crrev.com/494dcbfa7da1c0cd848a12212e096e015be0c024/chrome/browser/about_flags.cc
[modify] https://crrev.com/494dcbfa7da1c0cd848a12212e096e015be0c024/chrome/browser/resource_coordinator/tab_lifecycle_unit.cc
[modify] https://crrev.com/494dcbfa7da1c0cd848a12212e096e015be0c024/chrome/browser/resource_coordinator/tab_lifecycle_unit.h
[modify] https://crrev.com/494dcbfa7da1c0cd848a12212e096e015be0c024/chrome/browser/resource_coordinator/tab_lifecycle_unit_unittest.cc
[modify] https://crrev.com/494dcbfa7da1c0cd848a12212e096e015be0c024/chrome/browser/resource_coordinator/tab_manager_features.cc
[modify] https://crrev.com/494dcbfa7da1c0cd848a12212e096e015be0c024/chrome/browser/resource_coordinator/tab_manager_features.h
[modify] https://crrev.com/494dcbfa7da1c0cd848a12212e096e015be0c024/chrome/browser/resource_coordinator/tab_manager_features_unittest.cc