"...and we've just started using this technology on the Samsung ARM-Based Chromebook. Our player on this Chromebook device uses the Media Source Extensions and Encrypted Media Extensions to adaptively stream protected content."

I'm not an expert on Chrome OS internals but it seems to me that being a GNU/Linux derivative with an X Server, it's not much of a jump to say the Linux version is being developed and tested first.

Edit to clarify: I'm guessing the development is being done on a Linux machine rather than directly on a Chromebook.