Created attachment 1189791 [details]
strace of GNOME Screenshot

Description of problem:
After selecting an area to capture, GNOME Screenshot often hangs for 10-30 seconds before showing the screen that allows you to save the image or copy it to the clipboard.

Version-Release number of selected component (if applicable):
[straussd@titan ~]$ dnf info gnome-screenshot
Last metadata expiration check: 21 days, 23:06:09 ago on Tue Jul 19 13:49:27 2016.
Installed Packages
Name        : gnome-screenshot
Arch        : x86_64
Epoch       : 0
Version     : 3.20.1
Release     : 1.fc24
Size        : 855 k
Repo        : @System
From repo   : updates
Summary     : A screenshot utility for GNOME
URL         : http://www.gnome.org
License     : GPLv2+
Description : gnome-screenshot lets you take pictures of your screen.

How reproducible:
Every time I take a screenshot from Slack running in Chrome or Firefox.

Steps to Reproduce:
1. Log in with a Wayland session. (Not sure if this is relevant, but it's what I do.)
2. Load a busy channel in Slack. (For whatever reason, this seems to be relevant. Screenshots of, say, Bugzilla don't create any delay.)
3. Use GNOME Screenshot to snap part of the window. (Snapping the whole window doesn't cause a delay, either.)

Actual results:
Long delay before GNOME Screenshot steals my focus and then allows me to save the file.

Expected results:
Nearly instant option to save the file.

Additional info:
The strace is truncated and only contains data up to the hang (on the mmap call).