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/src/counter_metric.cpp

@@ -12,7 +12,7 @@ namespace metrics {
 
 void BaseCounterMetric::Increment(const std::string &counter_key,
                                   int64_t value) {
-  AutoLock lock(internal_lock_);
+  std::unique_lock<std::mutex> lock(internal_lock_);
 
   if (value_map_.find(counter_key) == value_map_.end()) {
     value_map_[counter_key] = value;