Merge from widevine repo of http://go/wvgerrit/17877
The final spec for CENC says that partial encrypted blocks are only
allowed for "cenc" mode, and not for "cens" mode. Also, the
pattern_offset must be 0 for all calls to OEMCrypto_DecryptCENC.
Review doc changes http://go/wvdelta11 and http://go/oemcrypto
Notice that this CL affects documentation and test code only. No
production code is affected.
b/28718266
b/28817376
Change-Id: I1d6a38a763a2b693ea0c26bc909e1c721b8facaf
0b2223018d