DrmManager: locally aggregate API metrics

Aggregate DrmManager API invocation counts per plugin over at least
fixed period of time before sending metrics to mediametrics service.

The default period is 1 day; the period is configurable through the
property drmmanager.metrics.period.

Bug: 134789967
Test: dumpsys media.metrics
Change-Id: I2cf28f1dfaa485ca319360705b872eed995b3d7f
diff --git a/drm/drmserver/DrmManagerService.h b/drm/drmserver/DrmManagerService.h
index 2e27a3c..f9b8bef 100644
--- a/drm/drmserver/DrmManagerService.h
+++ b/drm/drmserver/DrmManagerService.h
@@ -142,7 +142,7 @@
     virtual status_t dump(int fd, const Vector<String16>& args);
 
 private:
-    DrmManager* mDrmManager;
+    sp<DrmManager> mDrmManager;
 };
 
 };