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/core/include/cdm_engine.h

@@ -6,6 +6,7 @@
 #define WVCDM_CORE_CDM_ENGINE_H_
 
 #include <memory>
+#include <mutex>
 #include <string>
 #include <vector>
 
@@ -16,7 +17,6 @@
 #include "disallow_copy_and_assign.h"
 #include "file_store.h"
 #include "initialization_data.h"
-#include "lock.h"
 #include "metrics_collections.h"
 #include "oemcrypto_adapter.h"
 #include "service_certificate.h"
@@ -338,7 +338,7 @@ class CdmEngine {
   int64_t last_usage_information_update_time_;
 
   // Protect release_key_sets_ from non-thread-safe operations.
-  Lock release_key_sets_lock_;
+  std::mutex release_key_sets_lock_;
 
   // TODO(rfrias): Replace with two sets of locks, one to protect
   // the CdmSessionMap and a per-session lock to control access to
@@ -349,7 +349,7 @@ class CdmEngine {
   // The layer above the CDM implementation is expected to handle thread
   // synchronization to make sure other functions that access sessions do not
   // occur simultaneously with OpenSession or CloseSession.
-  Lock session_map_lock_;
+  std::mutex session_map_lock_;
 
   CORE_DISALLOW_COPY_AND_ASSIGN(CdmEngine);
 };