Specify parameters for launcher program

The easiest thing to do is:

1. Remove your existing Chrome icon from the Unity launcher
2. Open the Unity Dash and make it non-maximized

3. Type "chrome"
4. Drag the Chrome icon to your desktop
5. Right-click on the Chrome icon on your desktop and choose "Properties"
6. Modify "Command" to insert --scroll-pixels=50 before %U and close the window
7. Move the icon from your desktop to some folder (where it will stay)
8. Drag the icon from the folder to your Unity launcher

1. Type "chrome"
2. Drag the Chrome icon to your desktop
3. Find the name of chrome which is 'google-chrome.desktop' in my PC
4. sudo find / -name google-chrome.desktop, I found the location of the launch in /usr/share/applications/google-chrome.desktop
5. Modify the 'Exec' value
6. save and exit, rm the Chrome icon in your desktop

A simple way is to install alacarte, which is the old menu editor for Ubuntu.

sudo apt-get install alacarte

Simply run it, find the shortcut (Applications -> Internet -> Google Chrome), click Proprties, and add your argument to the command.

*note, this will change the shortcut both in the dash and launcher, which may or may not be what you want.