Chromium on Ubuntu 14.04 doesn't use Netscape plugin API anymore, it
simply not there.
The Chrome browser has support for Flash, so the following steps
download Chrome, extract it's Flashplayer and install it for Chromium.
You need to reboot your computer after installing to activate it, or
kill all running chromium-browser processes.
We need to install the Pepper Flash player installer.
$ sudo apt-get install pepperflashplugin-nonfree
$ sudo update-pepperflashplugin-nonfree --install
If you want to uninstall it for some reason, use
$ sudo update-pepperflashplugin-nonfree --uninstall