Use <code> rather than <tt> elements for HTML5-ification

Apparently some Blackbery devices just silently chomp content inside HTML4-style
elements, so let's use the HTML5 version (which is meant to be preferred anyway).

Bug: 67084
Change-Id: I7e07fc2193b290a0e5c3912a678f53045ff1de32
Merge "Use <code> rather than <tt> elements for HTML5-ification"