The Java APIs only easily expose getting the PSSH data blob, not the full PSSH
box. So that apps do not have to do extra work, wrapping the PSSH data blob in a
PSSH box again, we do it for them in the DrmPlugin.
Includes requisite changes to the Unit tests
Bug: 8584241
Merge of https://widevine-internal-review.googlesource.com/#/c/5142/
from the Widevine CDM repository.
Change-Id: Ifb5910dd52380e1b591ecdf1e4273c8d9f3294cc