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/tests/Android.bp b/drm/libmediadrm/tests/Android.bp
index 674d3eb..485e78c 100644
--- a/drm/libmediadrm/tests/Android.bp
+++ b/drm/libmediadrm/tests/Android.bp
@@ -10,3 +10,18 @@
       "-Wall",
     ],
 }
+
+cc_test {
+    name: "EventMetric_test",
+    srcs: ["EventMetric_test.cpp"],
+    shared_libs: [
+      "liblog",
+      "libmediadrm",
+      "libutils",
+    ],
+    include_dirs: ["frameworks/av/include/media"],
+    cflags: [
+      "-Werror",
+      "-Wall",
+    ],
+}