Refactored metrics to support pull model.

MetricsGroup split into 3 groups, session, engine, and crypto.
MetricsFrontEnd and Report removed.

This is a merge from wvgerrit/28420

Bug: 36217927
Test: Added unit tests to cover modified code.
Change-Id: I2f39f99ce88cc2229d6d1aa9459c67c5b86ccef4

libwvdrmengine/cdm/core/src/crypto_session.cpp

@@ -12,7 +12,6 @@
 
 #include "crypto_key.h"
 #include "log.h"
-#include "metrics_front_end.h"
 #include "openssl/sha.h"
 #include "properties.h"
 #include "pst_report.h"
@@ -45,7 +44,7 @@ uint64_t CryptoSession::request_id_index_ = 0;
 UsageTableHeader* CryptoSession::usage_table_header_l1_ = NULL;
 UsageTableHeader* CryptoSession::usage_table_header_l3_ = NULL;
 
-CryptoSession::CryptoSession(metrics::MetricsGroup* metrics)
+CryptoSession::CryptoSession(metrics::CryptoMetrics* metrics)
     : metrics_(metrics),
       open_(false),
       update_usage_table_after_close_session_(false),