This change creates a unique id in the cdm identifier in order to force
a one-to-one mapping between WVDrmPlugin instances and CDM Engines. This
change simplifies some assumptions. This includes ensuring that the
metrics for a given MediaDrm instance map to a given CdmEngine instance.
Bug: 73724453
Test: Updated unit tests. GTS test pass. Shaka Player, Netflix and Google Play test.
Change-Id: I7e041b6cdf3e272d067da49d25a297b4a4663f1f