Remove call to time.Now() on worker thread when handling record reqs (c…

…ensus-instrumentation#1210)

Time is already recorded on the client side and stored in the currently unused recordReq.t
field. Avoiding these repeated calls to time.Now while the worker is blocked can significantly
reduce worker contention.

stats/view/worker_commands.go

@@ -163,7 +163,7 @@ func (cmd *recordReq) handleCommand(w *worker) {
 		}
 		ref := w.getMeasureRef(m.Measure().Name())
 		for v := range ref.views {
-			v.addSample(cmd.tm, m.Value(), cmd.attachments, time.Now())
+			v.addSample(cmd.tm, m.Value(), cmd.attachments, cmd.t)
 		}
 	}
 }