Here is how I did to add a custom Google Chrome launcher to Unity in Ubuntu 12.04.
First I located a desktop launcher that I could use as a template for my new launcher.
$ locate google-chrome.desktop
The first result looked okay so I copied it to the desktop (You can also save it to /usr/share/applications/, that will make it available for all users and you won’t have to keep the icon on the desktop).
$ cp /home/steffe/.gnome2/panel2.d/default/launchers/google-chrome.desktop ~/Desktop/google-chrome-webgl.desktop
Next I did was to edit the file to make it the way I wanted. In my case I changed the variables Name and Exec in the file:
Name=Google Chrome with WebGL
Exec=/opt/google/chrome/google-chrome --enable-plugins --ignore-gpu-blacklist %U
The desktop launcher needs to be executable to run. Hence,
$ chmod +x ~/Desktop/google-chrome-webgl.desktop
Now the launcher should show up on the desktop. Drag and drop it onto the Unity panel. Done!