suspend on critical battery state can be prevented by applications

[Andreas E.]

Some applications prevent the computer from going to suspend mode (applications that display video, eg. chromium, opera, openshot) because they assume it is in the user's interest to keep the screen on even when inactive. This is most times helpful and saves the user from having to move a finger. But on low battery power, the user's inactivity could also be due to absence or sleep, and keeping the computer on until the power is 0.000% causes more damage than it serves the user's interest:
- battery drain over time
- data loss

We can not rely on that every application implements sophisticated power management in the user's interest and has no malicious intentions. It is crucial that the operating system still reserves to have the last word in resource and power management.

Steps to reproduce:
1. Watch a video in Opera (36) in full screen
2. Fall asleep
3. After some hours, the computer is either still on (with battery <3%) or already off

Expected behavior:
When not connected to an external power source and battery has low power (<30%), the usual procedure for suspend is still applied:
1. Notification on inactivity
2. Suspend

There may be a way to configure this manually, but I think due to the implications of hardware drain and data loss Ubuntu should come with a reasonable default that serves the interests of general, unconscious users.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: gnome-power-manager 3.16.1-1ubuntu1
Uname: Linux 4.2.0-040200rc3-generic x86_64
ApportVersion: 2.19.1-0ubuntu5
Architecture: amd64
CurrentDesktop: Unity
Date: Fri Apr 15 07:49:47 2016
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-06-06 (313 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
SourcePackage: gnome-power-manager
UpgradeStatus: No upgrade log present (probably fresh install)