[ Merge of http://go/wvgerrit/25643 ]
The MediaDrm#provideKeyResponse API states that an empty byte array is
returned when the license type is streaming or release but a non-empty
value was being returned in some cases.
The KeySetId is now returned when the license type is offline or when
the license is streaming and has a secure stop associated with it.
Test: Verified by request_license_test integration tests. Tests have been
modified to validate the returned Key Set Id values.
b/36093612
Change-Id: I82dba537c77ddd1d1876cbce58729f3db901ee51
5321b96623