Help with scripting a nameless window

[zfgxdfgdfg]

Hi! So up until Yosemite, I've been using an AppleScript to automatically resize the Buddies window of Messages as people go on and offline. But as of Yosemite, the "Buddies" window is no longer called "Buddies". In fact, it doesn't have a title (rather, it's title is ""). The message window also doesn't have a title. So I can't just change my script to act on the window "", because it still might not act on the right one.

Is there any other way someone knows of I can act on this window? The window ID isn't consistent across sessions, so that won't work.

Thanks!