Add Lock to ValueMetric

(This is a merge of http://go/wvgerrit/72723)

ValueMetric, unlike the other metrics, was not safe to call from
multiple threads. This patch adds internal locking to ValueMetric to
ensure its safety.

Bug: 124459322
Bug: 70889998
Bug: 118584039
Test: CE CDM Unit Tests
Test: Android Unit Tests
Change-Id: I55855ba8a5cdb2bbe1e15be7742304293245b5aa

libwvdrmengine/cdm/metrics/include/value_metric.h

@@ -6,6 +6,7 @@
 #define WVCDM_METRICS_VALUE_METRIC_H_
 
 #include <stdint.h>
+#include <mutex>
 #include <string>
 
 #include "metrics.pb.h"
@@ -46,6 +47,7 @@ class ValueMetric {
 
   // Record the value of the metric.
   void Record(const T &value) {
+    std::unique_lock<std::mutex> lock(internal_lock_);
     value_ = value;
     has_value_ = true;
     has_error_ = false;
@@ -53,19 +55,33 @@ class ValueMetric {
 
   // Set the error code if an error was encountered.
   void SetError(int error_code) {
+    std::unique_lock<std::mutex> lock(internal_lock_);
     error_code_ = error_code;
     has_value_ = false;
     has_error_ = true;
   }
 
-  bool HasValue() const { return has_value_; }
-  const T &GetValue() const { return value_; }
+  bool HasValue() const {
+    std::unique_lock<std::mutex> lock(internal_lock_);
+    return has_value_;
+  }
+  const T &GetValue() const {
+    std::unique_lock<std::mutex> lock(internal_lock_);
+    return value_;
+  }
 
-  bool HasError() const { return has_error_; }
-  int GetError() const { return error_code_; }
+  bool HasError() const {
+    std::unique_lock<std::mutex> lock(internal_lock_);
+    return has_error_;
+  }
+  int GetError() const {
+    std::unique_lock<std::mutex> lock(internal_lock_);
+    return error_code_;
+  }
 
   // Clears the indicators that the metric or error was set.
   void Clear() {
+    std::unique_lock<std::mutex> lock(internal_lock_);
     has_value_ = false;
     has_error_ = false;
   }
@@ -73,6 +89,7 @@ class ValueMetric {
   // Returns a new ValueMetric proto containing the metric value or the
   // error code. If neither the error or value are set, it returns nullptr.
   drm_metrics::ValueMetric *ToProto() const {
+    std::unique_lock<std::mutex> lock(internal_lock_);
     if (has_error_) {
       drm_metrics::ValueMetric *value_proto = new drm_metrics::ValueMetric;
       value_proto->set_error_code(error_code_);
@@ -91,6 +108,16 @@ class ValueMetric {
   int error_code_;
   bool has_error_;
   bool has_value_;
+
+  /*
+   * This locks the internal state of the value metric to ensure safety
+   * across multiple threads preventing the caller from worrying about
+   * locking.
+   *
+   * This field must be declared mutable because the lock must be takeable even
+   * in const methods.
+   */
+  mutable std::mutex internal_lock_;
 };
 
 }  // namespace metrics