(This is a merge of http://go/wvgerrit/12700 from the Widevine CDM
repository.)
Adds unit tests which cover several cases, including five which are
fixed in this patch:
* Find a Widevine PSSH after a PSSH with non-zero flags.
(We have no control over another provider's abuse of the flags field,
so we should not give up if such a PSSH appears before ours.)
* Find a Widevine PSSH after a v1 PSSH.
(CENC now specifies a general v1 format. We don't have to support it
directly in the CDM, but we do have to skip it gracefully.)
* Find a Widevine PSSH after a non-PSSH box.
(This would be unusual input, but we can easily recover from it.)
* Parse a PSSH box with a size field of 0, which means "the rest of the
buffer."
(This would be unusual input, too, but is technically allowed for any
MP4 box.)
* Parse a v1 Widevine PSSH box, ignoring the new fields we don't need.
Bug: 19288007
Change-Id: I355df9e34ba4d53cc02e8501de965a0d193ee554
4252a4b790