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/cdm/test/Android.mk

@@ -21,6 +21,11 @@ test_src_dir := ../core/test
 test_main := ../core/test/test_main.cpp
 include $(LOCAL_PATH)/integration-test.mk
 
+test_name := cdm_engine_metrics_decorator_unittest
+test_src_dir := ../core/test
+test_main := ../core/test/test_main.cpp
+include $(LOCAL_PATH)/integration-test.mk
+
 test_name := cdm_extended_duration_test
 test_src_dir := .
 test_main := ../core/test/test_main.cpp