Perpetual zoom

[snblickhan]

Using Chrome (64-bit) on OS X El Capitan 10.11.6. Zooming into an image, zoom got stuck (going all the way to full zoom; if I tried to zoom back out it would keep zooming back in). Apparently this has happened before, there's a Talk thread about it. A user triggered this bug by clicking on the zoom button and moving cursor off the button whilst still holding it down. I tried that, and it seems to be what's causing the problem.