It appears to me that Chrome somehow 'ignores' font-size of <code>'s first preceding element (<pre>), which has its font-size set to 13px, which would result in <code>'s computed font-size to be 10.4px, not 12.8px (resulting from 16*0.8).
It's rather odd… here's the video recording: http://recordit.co/0AYbaF6WCa
Although computed value is 13px, it has zero effect on typography of its child elements, unless you manually set the font-size to 13px.
@zpao That would be my guess, yes.
I'll take another look today, it was way past midnight last night, so I may have missed something. Either way, I'l like to get to the bottom of this issue and report a bug to Chrome if necessary.