Add metrics_dump, a tool to format drm metrics

[ Merge of http://go/wvgerrit/59022 ]

Android metrics are output by the adb shell command
|dumpsys media.metrics|. They appear in bugreports
and can also be requested interactively. Both the
widevine and framework mediadrm metrics are base64
encoded protobufs detailing each of the metrics
items. This tool prints them in a readable format.

Test: wv android unit/integration tests
Change-Id: Id1bc05b34693a3ca44dd3872a28a2337b3ce4d79

libwvdrmengine/tools/metrics_dump/include/wv_metrics.h

@@ -0,0 +1,14 @@
+// Copyright 2018 Google LLC. All Rights Reserved. This file and proprietary
+// source code may only be used and distributed under the Widevine Master
+// License Agreement.
+//
+// Format widevine protobuf metrics
+
+#include <string>
+
+#include "metrics.pb.h"
+
+namespace wv_metrics {
+void FormatWvCdmMetrics(const drm_metrics::WvCdmMetrics& metrics,
+                        std::string& result);
+};