Improve splash screen behaviour

[Michał Sawicz]

Related to bug #1577641, we may want to improve the way the splash screen logic is implemented.

The shell-managed splash screens serve as a way to provide immediate feedback for an application being launched, so that the user doesn't need to find out whether they failed to launch the app or the app's just slow to launch (or maybe even crashed on startup).

My proposal is that:
- we delay showing the splash screen for a very short interval (50ms to start with?)
- *if* the splash screen is shown, it has to be shown for at least a certain time (500ms?) to avoid "flicker" between the splash screen and the app surface
- if possible, let the user know that the app crashed/exited with an error and give the user an option to restart or close (long-term maybe also report the issue?)

ProblemType: Bug
DistroRelease: Ubuntu 17.04
Package: unity8 8.15+17.04.20170303.1-0ubuntu1 [origin: LP-PPA-ci-train-ppa-service-2481]
ProcVersionSignature: Ubuntu 4.10.0-9.11-generic 4.10.0
Uname: Linux 4.10.0-9-generic x86_64
NonfreeKernelModules: zfs zunicode zavl zcommon znvpair
ApportVersion: 2.20.4-0ubuntu2
Architecture: amd64
CurrentDesktop: Unity:Unity7
Date: Mon Mar 6 18:33:05 2017
InstallationDate: Installed on 2016-05-06 (303 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
SourcePackage: unity8
UpgradeStatus: Upgraded to zesty on 2016-11-22 (104 days ago)

[Daniel d'Andrada (dandrader)]

The biggest problem with splash screens is on desktop: the first time an application is launched Unity8 has no idea of its window constraints (minimum, maximum and preferred sizes) so that it can choose an adequate size for the splash screen.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Michał Sawicz (saviq)]

Sure, but it will resize to the right size once it knows it (even before the application draws).

We could also give the ability to configure the preferred splash screen size.