Introduce common::ToSeconds for std::chrono::steady_clock::duration. (#1244)

Introduce a new overload of ToSeconds for std::chrono::steady_clock and use it for the work queue delay metric.

cartographer/common/time.cc

@@ -31,6 +31,11 @@ double ToSeconds(const Duration duration) {
       .count();
 }
 
+double ToSeconds(const std::chrono::steady_clock::duration duration) {
+  return std::chrono::duration_cast<std::chrono::duration<double>>(duration)
+      .count();
+}
+
 Time FromUniversal(const int64 ticks) { return Time(Duration(ticks)); }
 
 int64 ToUniversal(const Time time) { return time.time_since_epoch().count(); }

cartographer/common/time.h

@@ -49,6 +49,7 @@ Duration FromMilliseconds(int64 milliseconds);
 
 // Returns the given duration in seconds.
 double ToSeconds(Duration duration);
+double ToSeconds(std::chrono::steady_clock::duration duration);
 
 // Creates a time from a Universal Time Scale.
 Time FromUniversal(int64 ticks);

cartographer/mapping/internal/2d/pose_graph_2d.cc

@@ -151,9 +151,7 @@ void PoseGraph2D::AddWorkItem(const std::function<void()>& work_item) {
     const auto now = std::chrono::steady_clock::now();
     work_queue_->push_back({now, work_item});
     kWorkQueueDelayMetric->Set(
-        std::chrono::duration_cast<std::chrono::duration<double>>(
-            now - work_queue_->front().time)
-            .count());
+        common::ToSeconds(now - work_queue_->front().time));
   }
 }
 

cartographer/mapping/internal/3d/pose_graph_3d.cc

@@ -149,9 +149,7 @@ void PoseGraph3D::AddWorkItem(const std::function<void()>& work_item) {
     const auto now = std::chrono::steady_clock::now();
     work_queue_->push_back({now, work_item});
     kWorkQueueDelayMetric->Set(
-        std::chrono::duration_cast<std::chrono::duration<double>>(
-            now - work_queue_->front().time)
-            .count());
+        common::ToSeconds(now - work_queue_->front().time));
   }
 }