Discharging static electricity touching chassis macbook pro?
Yes, and it is common practice in the PC industry to 'ground' yourself on the PC chassis (make sure it is the chassis). This negates any charge (and voltage) between you and the device. This will offer better protection than say, grabbing a RAM module and having the discharge path between you and the device go through the pins of the RAM module (and potentially knock out some transistors along the way).

However, grounding oneself on the chassis will not prevent other sources of ESD that include:
1) Fields from clothing or other materials that generate static (and hold a static charge, wood, clothing, paper, most plastics).
2) Will not equalize the potential between the PC and ground or you and ground.  

So the best way would be to wear a wrist strap connected to ground, and place the device on an ESD mat that is grounded thus keeping all objects at a 0V potential. And also keeping the potential between objects at 0V (0V-0V = 0V) (and if your really cool you get an esd lab coat that shields your clothes)   

A better way is ground oneself on the chassis (and keep contact through the duration of the repair) OR ground a wrist strap to the chassis (contact all the time)

And the worst way is to not ground yourself at all and have the grounding path go directly to a component on the PCB (via screwdriver) or through a component you are installing. 

In ESD controlled environments there is much more to it then simply grounding yourself on the Chassis, but this is not possible for most people who just want to install a module.