Add EventMetric and a single use case.

Adds an EventMetric class, associated unit tests, and an instance of the
EventMetric to DrmHal. Also added a unit test for CounterMetric and
created a class to hold all of the future metric instances.

BUG: 64001676

Test: Added and ran unit tests.  Also added a CTS test case.
Change-Id: Ic94bedd5f8293a58a939613a4ae69ce656a772be
diff --git a/drm/libmediadrm/Android.bp b/drm/libmediadrm/Android.bp
index 2e8da4b..ea239c5 100644
--- a/drm/libmediadrm/Android.bp
+++ b/drm/libmediadrm/Android.bp
@@ -18,6 +18,7 @@
         "PluginMetricsReporting.cpp",
         "SharedLibrary.cpp",
         "DrmHal.cpp",
+	"DrmMetrics.cpp",
         "CryptoHal.cpp",
         "protos/plugin_metrics.proto",
     ],