These files create transparent replacement for the graphics files of the background, border, and tail of chat bubbles. They make your chat bubbles well transparent (text only).
Until Blizzard decides to redo the images for these, this will continue to work without having to run any addon that modifies the chat bubble frame (these tend to taint and bug every patch so this method is far less invasive).
To use this, simply download the images, extract the tooltip folder, close your game client, and place within your interface folder (not the addon folder within). That's it. If you want to restore your chat bubbles, simply delete the tooltip folder and relaunch your game client.
So it will be: World of Warcraft\Interface\Tooltips
This comes as is but should work regardless of patches (until Blizzard one day changes these images that is). Should Blizzard change the structure of the chat bubble graphics, this will no longer work and may be abandoned. ;)