Google crome but an window over another?

Let's say I want to watch a Stream of a video clip on youtube and play wow in the background, then i want to be able to klick around on WoW but still have my internet page of google crome stream in front of my wow window, how to?|||You can have the youtube already opened then play WoW, but since WoW dont have a window mode, then just press Alt + tab then it let you choose on what window you want to check, then click WoW again, but you cant have them side by side since WoW dont have a window mode like I said.