(Merge from http://go/wvgerrit/29180) initDataResemblesPSSH was not checking if the buffer was large enough to contain the PSSH markers that it was looking for. Consequently, it could read data past the end of the buffer. Bug: 63076692 Test: Unit Tests Test: Google Play Movies Change-Id: I6a4a3fa4b05d98554645f3c3149569702c96fd66