Creates a new license request latency metric

Previously, we did not have a license request latency metric. This is a
notable limitation in our metrics. This adds a metric that captures the
timing between a GenerateKeyRequest and an AddKey operation.

Bug: 72994956
Test: New unit tests. Google Play
Change-Id: If99c187399c02f9b5d4c355732af7588bbbefb11

libwvdrmengine/cdm/metrics/src/attribute_handler.cpp

@@ -72,6 +72,14 @@ void SetAttributeField<drm_metrics::Attributes::kSigningAlgorithmFieldNumber,
   attributes->set_signing_algorithm(signing_algorithm);
 }
 
+template <>
+void SetAttributeField<drm_metrics::Attributes::kKeyRequestTypeFieldNumber,
+                       CdmKeyRequestType>(
+    const CdmKeyRequestType &key_request_type,
+    drm_metrics::Attributes *attributes) {
+  attributes->set_key_request_type(key_request_type);
+}
+
 template <>
 void SetAttributeField<0, util::Unused>(const util::Unused &,
                                         drm_metrics::Attributes *) {