After downloading  and install flash plugin

you need to copy libflashplayer.so to chromium folder like below

$sudo cp /usr/lib/flashplugin-installer/libflashplayer.so /usr/lib/chromium-browser/plugins

or

you can create a symlink

$sudo ln -s /usr/lib/flashplugin-installer/libflashplayer.so /usr/lib/chromium-browser/plugins/

and run below command

$chromium-browser –enable-plugins