Merge from widevine repo of http://go/wvgerrit/20660 For CTR encryption mode, when a subsample ends with partial block that is continued on the next subsample, both blocks should have the same IV. This allows an implementation of OEMCrypto to optimize their decryption algorithm. b/31114392 Change-Id: I29a998b00f3bfb12c4bbbcb1fa1ebc371473fefd