Has the browser closed without my intending for it to happen, with other sites? Yes.

It hasn't happened often enough where I have been able to figure out if it is something I did just prior to this happening, and thus it was my actions as the cause, or if it was a crash and the browser just disappeared. I have a touchpad that I'm always bumping as I type causing the mouse to click somewhere where I didn't intend. If that's the cause (e.g., clicking the X to close the browser), then I wish Chrome would let me configure it to make me confirm that I really want to close the browser (even if I have multiple tabs open).