confirm('foobar') in JSFiddle, until I kill all instances of chrome.exe.
My current instance of Chrome is now in that state. (I learned to "escape" by hitting TabEnter to select Cancel on the invisible confirmation dialog, but this only works if the offending dialog occurs on the window and tab that happened to be active.)
What can I do to gather information about the state of Chrome to report this bug? Nothing appears on the Developers' console. This has been happening for about a year now, and since then I've reinstalled Chrome on 3 of my machines (2 of them on clean Windows 7 installations), yet I run into this issue on all machines. I think I happen to notice them more than most because I play an online game that makes use of confirmation dialogs between turn actions, but the issue isn't specific to that site—I've experienced it on other sites, and as I said, I can reproduce it on JSFiddle once it happens once.