Currently the CDM requires the caller to specify init data both on key
generation and renewal requests. With this change the CDM relaxes
this requirement for renewals.
Bug: 8732893
Merge of https://widevine-internal-review.googlesource.com/#/c/5322/
from Widevine CDM repo
Change-Id: Idf4ad2bdb20023da4f30bc369ed87eb811c1c4d9