The EME spec technically requires CDMs to treat audio/mp4 and
video/mp4 equivalently, as well as audio/webm and video/webm. We had
only been accepting video/mp4 and video/webm up until now.
This change also centralizes handling of init data types in the shared
CDM code instead of having it spread across multiple places in the
codebase.
(This is a merge of https://widevine-internal-review.googlesource.com/9532/
from the Widevine CDM repo.)
Bug: 13564917
Change-Id: Ib8bdfb2b003ffb00e8f0559561335abb3c5778b0
7eea20df86