[ Merge from http://go/wvgerrit/69105 ]
This adds a metric collecting decorator class around cdm engine. This
implementation uses a templated decorator. The decorator enables:
1) Wrapping the CDM Engine methods to capture timing and error
information.
2) Allows use of a mock CDM Engine for testing.
Test: Unit tests. GPlay manual testing and GTS tests.
BUG: http://b/64724336
Change-Id: I5e4a0f552974fab1939bc7ab02719a1f5849cf3f
46eecb6b80