CDM Metrics Protocol buffer serialization.

An implementation that serializes metrics to a protocol buffer.

This is a merge from wvgerrit/28440.

I intend to submit 2048751, 2048750, and 2048509 together.

Bug: 36217927
Bug: 36220975
Test: Added unit tests to cover modified code.
Change-Id: Ie8b9d8b91d2602b015f5568890a16c0419c126df

libwvdrmengine/cdm/metrics/src/metrics.proto

@@ -0,0 +1,36 @@
+// Copyright 2017 Google Inc. All Rights Reserved.
+//
+// This file contains a proto definition for serialization of metrics data.
+//
+syntax = "proto2";
+
+package drm_metrics;
+
+// need this if we are using libprotobuf-cpp-2.3.0-lite
+option optimize_for = LITE_RUNTIME;
+
+// The MetricsGroup is a collection of metric name/value pair instances
+// that can be serialized and provided to a caller.
+message MetricsGroup {
+  message Metric {
+    message MetricValue {
+      // Only one of the following values must be set. Note that the oneof
+      // keyword is not supported in the protobuf version checked into the CDM.
+      optional int64 int_value = 1;
+      optional double double_value = 2;
+      optional string string_value = 3;
+    }
+
+    // The name of the metric. Must be valid UTF-8. Required.
+    optional string name = 1;
+
+    // The value of the metric. Required.
+    optional MetricValue value = 2;
+  }
+
+  // The list of name/value pairs of metrics.
+  repeated Metric metric = 1;
+
+  // Allow multiple sub groups of metrics.
+  repeated MetricsGroup metric_sub_group = 2;
+}