Add a metric decorator around cdm engine

[ 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

libwvdrmengine/build_and_run_all_unit_tests.sh

@@ -83,6 +83,7 @@ try_adb_push() {
 try_adb_push base64_test
 try_adb_push buffer_reader_test
 try_adb_push cdm_engine_test
+try_adb_push cdm_engine_metrics_decorator_unittest
 try_adb_push cdm_feature_test
 try_adb_push cdm_extended_duration_test
 try_adb_push cdm_session_unittest