I also made a search about the meaning and found that in fact Google is celebrating the 30th anniversary of Pac-man. Google has been creating different kinds of logos to celebrate different occasions of the world since 1998 until now. The custom homepage logo is called doodle. You can see the collection of Google custom logos by clicking this link.

But the logo I have seen today is the most different one. Why I said so? You can the "Insert Coin" button when you open the homepage. When you click the button, you can play the game. And this seems to be the first playable version of the doodle.