Change from custom Lock to std::mutex.

[ Merge of http://go/wvgerrit/67884 ]

Now that we can use C++11, we should use the cross-platform std::mutex
type, not the custom pthread version.

Bug: 111850982
Test: WV unit/integration tests
Change-Id: If2fde2836826c5184609e6b1f3a6511206bd4594

libwvdrmengine/cdm/metrics/include/metrics_collections.h

@@ -8,6 +8,7 @@
 
 #include <stddef.h>
 #include <stdint.h>
+#include <mutex>
 #include <ostream>
 
 #include "OEMCryptoCENC.h"
@@ -313,7 +314,7 @@ class OemCryptoDynamicAdapterMetrics {
   void Clear();
 
  private:
-  mutable Lock adapter_lock_;
+  mutable std::mutex adapter_lock_;
   ValueMetric<OEMCryptoInitializationMode> oemcrypto_initialization_mode_;
   ValueMetric<uint32_t> oemcrypto_l1_api_version_;
   ValueMetric<uint32_t> oemcrypto_l1_min_api_version_;
@@ -405,7 +406,7 @@ class EngineMetrics {
       cdm_engine_unprovision_;
 
  private:
-  mutable Lock session_metrics_lock_;
+  mutable std::mutex session_metrics_lock_;
   std::vector<metrics::SessionMetrics *> session_metrics_list_;
   // This is used to populate the engine lifespan metric
   metrics::TimerMetric life_span_internal_;