mozilla/pdf.js — pull request #5104 by Rob--W (2014-07-30 21:12:33+00:00)
Title: Use CSS.supports instead of '..' in ....style

`document.documentElement.style` is null in some XML documents.
The previous snippet caused the following error:

> Uncaught TypeError: Cannot use 'in' operator to search for 'animation' in null

To fix this bug, `'animation' in document.documentElement.style` has been replaced with `CSS.supports('animation', '9s')`.