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/src/distribution.cpp

@@ -3,27 +3,15 @@
 // Agreement.
 //
 // This file contains the definitions for the Distribution class members.
-
 #include "distribution.h"
 
-#include <float.h>
-
 namespace wvcdm {
 namespace metrics {
-Distribution::Distribution()
-    : count_(0ULL),
-      min_(FLT_MAX),
-      max_(-FLT_MAX),
-      mean_(0.0),
-      sum_squared_deviation_(0.0) {}
-
 void Distribution::Record(float value) {
   // Using method of provisional means.
-  float deviation = value - mean_;
-  mean_ = mean_ + (deviation / ++count_);
-  sum_squared_deviation_ =
-      sum_squared_deviation_ + (deviation * (value - mean_));
-
+  const float deviation = value - mean_;
+  mean_ += (deviation / ++count_);
+  sum_squared_deviation_ += (deviation * (value - mean_));
   min_ = min_ < value ? min_ : value;
   max_ = max_ > value ? max_ : value;
 }

libwvdrmengine/cdm/metrics/src/timer_metric.cpp

@@ -5,19 +5,26 @@
 
 namespace wvcdm {
 namespace metrics {
-void TimerMetric::Start() {
-  start_ = clock_.now();
+using ClockType = std::chrono::steady_clock;
+using TimePoint = std::chrono::time_point<ClockType>;
+
+void Timer::Start() {
+  start_ = ClockType::now();
   is_started_ = true;
 }
 
-void TimerMetric::Clear() { is_started_ = false; }
+void Timer::Clear() { is_started_ = false; }
 
-double TimerMetric::AsMs() const {
-  return (clock_.now() - start_) / std::chrono::milliseconds(1);
+double Timer::AsMs() const {
+  if (!is_started_) return 0.0;
+  const TimePoint end = ClockType::now();
+  return (end - start_) / std::chrono::milliseconds(1);
 }
 
-double TimerMetric::AsUs() const {
-  return (clock_.now() - start_) / std::chrono::microseconds(1);
+double Timer::AsUs() const {
+  if (!is_started_) return 0.0;
+  const TimePoint end = ClockType::now();
+  return (end - start_) / std::chrono::microseconds(1);
 }
 }  // namespace metrics
 }  // namespace wvcdm