StockMenu was creating a container for the sole purpose of applying style to
PopupMenu. Now we just use a StyleNode.
Also, I've reverted the change to make box-sizing default to border-box. It
turns out that CL wasn't effective because we didn't use the initialBoxSizing
function to initialize box sizing. I've made us use initialBoxSizing but switch
the default back to content-box because actually using border-box breaks a
bunch of stuff.
R=eseidel@chromium.org
Review URL: https://codereview.chromium.org/1024083003
f8b3596df6