Still unclear if it is going to be an actual feature in the next stable release of Google’s web browser, but if you open Chrome 20 beta in the experimental features’ page — by typing chrome://flags in the address bar –, down at the bottom of the list, you’ll find a new feature called Stacked Tabs.
Basically “Stacked Tabs” keeps tabs always at the same size, when Chrome reaches the amount of open tabs that can display correctly, they’ll get stack on top of each other. You can cycle between them by clicking the edge of the stacked tabs and you’ll notice as you cycle that tabs will start to stack up in the other end of the web browser as well.
By default this feature is disable, to turn it on simply click the Enable link and restart.
I personally would like to see Stacked Tabs as an actual feature in the next release of Google Chrome. Opera had something similar for a while now, where you simply drag & drop open tabs in top of each other to create a stack, but in Chrome this is now automatic.