If you're smart enough to use Github, you're smart enough to understand that "source code I can easily copy" does <i>not</i> mean "source code I am allowed to use if it is cool enough".
Namco has used the Pacman franchise for a lot, even the original version. It's not even close to the ethical grey-area of abandonware (but not legal-grey, abandonware is still considered copyright violation, it's just not expected to be enforced). The Wikipedia article linked seems to indicate that the original Google version was an authorized clone, but that doesn't make any copies and extensions that you make off of it authorized. There are so many minefields on this, and such games are so easy to make, that you might as well just leave this well enough alone.
And for those of you who just want to play and not bother with the source, Google still hosts the game "legally" at :<p><a href="http://www.google.com/pacman/" rel="nofollow">http://www.google.com/pacman/</a>
Check out a Google Pacman Level Editor. <a href="http://www.youtube.com/watch?v=_Jj3-NGO7xo" rel="nofollow">http://www.youtube.com/watch?v=_Jj3-NGO7xo</a>