Due to font-weight: bold; being set in .diffchange { font-weight: bold; }, the diff never renders any emoji characters on lines that are changed. This makes it easier for emoji spam to evade the eye of patrollers.
At least in Chrome/Mac, emoji characters aren't shown as they don't have a bold equivalent.
Upstream: https://code.google.com/p/chromium/issues/detail?id=441946