Registration Timeout is Excessively Long

I'm suffering from a problem where gnome-session pauses for a very long time (90 seconds) during login. I type in my password to lightdm, the screen switches to show my wallpaper, but nothing else, and for the next minute and a half, I can't do anything besides move the cursor. Clicks don't do anything, key combinations to start a terminal don't work. In /var/log/syslog, I see a message

Jun 23 11:24:21 jun-MacBookAir gnome-session[1591]: gnome-session-binary[1591]: WARNING: Application 'at-spi-dbus-bus.desktop' failed to register before timeout

which seems to be caused by a problem with at-spi-dbus-bus.desktop, but this bug report is not about that. The bug I'd like to report here is that gnome-session's timeout is *way* too long. At first I had no idea that the login was going to succeed at all, because it was frozen for so long, and I kept rebooting by pushing the power button.

The 90-second wait seems to be hard-coded in the source, with a remark that waiting long enough is critical on slower media like CD-ROMs. While I can see how that's a concern, it makes no sense on a desktop installation booting from the SSD. The long wait interferes with debugging the problem (because every single thing I try takes at least 90 seconds), and will ensure that a problem in any of the components like at-spi-dbus-bus.desktop will show up as a serious inconvenience. I for one cannot stand a computer that takes minutes to boot, just because one component is acting erratically.

Please make this timeout shorter if at all possible, or at least configurable. Better yet, please have this automatically configured by benchmarking the system upon installation.

In the meantime, I'm attaching a patch for anyone who wants a quick work around to this nasty problem.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: gnome-session 3.18.1.2-1ubuntu1.16.04.1
ProcVersionSignature: Ubuntu 4.4.0-24.43-generic 4.4.10
Uname: Linux 4.4.0-24-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CurrentDesktop: GNOME
Date: Thu Jun 23 13:07:40 2016
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-11-12 (223 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
PackageArchitecture: all
SourcePackage: gnome-session
UpgradeStatus: Upgraded to xenial on 2016-05-28 (25 days ago)