Updated metric Distribution and Timer utils.

[ Merge of http://go/wvgerrit/137811 ]

Renamed TimerMetric to Timer.  Timer is used to generate durations
included in metrics, but is not a metric itself.  The method of
getting the current time did not require creating an instance of
std::steady_clock.

Updated Distribution and Timer to use default initializers instead of
constructor initialization list.

Bug: 204946540
Test: Metric unit tests
Change-Id: I7ed291b586347dd0b7ab305960883bec04637315

libwvdrmengine/cdm/metrics/include/distribution.h

@@ -4,12 +4,12 @@
 //
 // This file contains the definition of a Distribution class which computes
 // the distribution values of a series of samples.
-
 #ifndef WVCDM_METRICS_DISTRIBUTION_H_
 #define WVCDM_METRICS_DISTRIBUTION_H_
-
 #include <stdint.h>
 
+#include <limits>
+
 namespace wvcdm {
 namespace metrics {
 // The Distribution class holds statistics about a series of values that the
@@ -25,7 +25,7 @@ namespace metrics {
 //   dist.Count();  // Returns 2.
 class Distribution {
  public:
-  Distribution();
+  Distribution() {}
 
   // Uses the provided sample value to update the computed statistics.
   void Record(float value);
@@ -41,11 +41,11 @@ class Distribution {
   }
 
  private:
-  uint64_t count_;
-  float min_;
-  float max_;
-  float mean_;
-  double sum_squared_deviation_;
+  uint64_t count_ = 0;
+  float min_ = std::numeric_limits<float>::max();
+  float max_ = std::numeric_limits<float>::lowest();
+  float mean_ = 0.0f;
+  double sum_squared_deviation_ = 0.0;
 };
 }  // namespace metrics
 }  // namespace wvcdm