It turns out the array of things certain apps pass as the MIME type is
greater than we believed. To support this, we will treat anything that
is not a known type as video/mp4 to mimic old behavior.
(This is a merge of https://widevine-internal-review.googlesource.com/9636
from the Widevine CDM repo.)
Bug: 13750843
Change-Id: I4b7bbe7d266ade9b35c6c5beb21502bf0715b854