Available as a snap package :
sudo apt-get install snapd
sudo snap install chromium
snap run chromium
However it seems to be rather unstable, and does not appear on the raspberry pi menu system. Complains about missing symbols on startup, and sometimes about the namespace of the mounted snap folder. Snap packages are put together by Canonical and not by Debian or the Raspberry Pi foundation. Typing this in Chromium 71.0.3578.98 on a PI 3.
Chromium snap info - https://uappexplorer.com/snap/ubuntu/chromium
Intro to snaps - https://tutorials.ubuntu.com/tutorial/basic-snap-usage#0
Most snaps are exclusive to AMD64 architectures, however the Chromium snap will run on Intel32 and armhf (Raspberry PI CPU)
pi@raspberrypi:~ $ snap list
Name Version Rev Tracking Publisher Notes
chromium 71.0.3578.98 569 stable canonical✓ -
core 16-2.37 6260 stable canonical✓ core
core18 18 596 stable canonical✓ base
gtk-common-themes 0.1-4-g88bc1b2 818 stable canonical✓ -
hello-world 6.3 27 stable canonical✓ devmode