trace2: fix child process time recording

Currently, we are recording child process times incorrectly for the
performance format target. This change fixes that by:

1. Ensuring we're recording the absolute time in child_start messages for
the performance format target, which we previously were not doing.
2. Ensures we do not conflate the absolute and relative times in
child_exit, which we were previously doing.

Author: ldennington

src/shared/Core/Trace2.cs

@@ -103,14 +103,14 @@ void WriteChildStart(DateTimeOffset startTime,
     /// <summary>
     /// Writes information related to exit of child process to trace writer.
     /// </summary>
-    /// <param name="elapsedTime">Runtime of child process.</param>
+    /// <param name="relativeTime">Runtime of child process.</param>
     /// <param name="pid">Id of exiting process.</param>
     /// <param name="code">Process exit code.</param>
     /// <param name="sid">The child process's session id.</param>
     /// <param name="filePath">Path of the file this method is called from.</param>
     /// <param name="lineNumber">Line number of file this method is called from.</param>
     void WriteChildExit(
-        double elapsedTime,
+        double relativeTime,
         int pid,
         int code,
         [System.Runtime.CompilerServices.CallerFilePath]
@@ -232,12 +232,13 @@ public void WriteChildStart(DateTimeOffset startTime,
             Classification = processClass,
             UseShell = useShell,
             Argv = procArgs,
-            Depth = ProcessManager.Depth
+            ElapsedTime = (DateTimeOffset.UtcNow - _applicationStartTime).TotalSeconds,
+            Depth = ProcessManager.Depth,
         });
     }
 
     public void WriteChildExit(
-        double elapsedTime,
+        double relativeTime,
         int pid,
         int code,
         string filePath = "",
@@ -262,7 +263,8 @@ public void WriteChildExit(
             Id = _childProcCounter,
             Pid = pid,
             Code = code,
-            ElapsedTime = elapsedTime,
+            ElapsedTime = (DateTimeOffset.UtcNow - _applicationStartTime).TotalSeconds,
+            RelativeTime = relativeTime,
             Depth = ProcessManager.Depth
         });
     }

src/shared/Core/Trace2Message.cs

@@ -266,6 +266,8 @@ public class ChildStartMessage : Trace2Message
     [JsonProperty("argv")]
     public IList<string> Argv { get; set; }
 
+    public double ElapsedTime { get; set; }
+
     public override string ToJson()
     {
         return JsonConvert.SerializeObject(this,
@@ -288,7 +290,7 @@ public override string ToPerformanceString()
 
     protected override string BuildPerformanceSpan()
     {
-        return EmptyPerformanceSpan;
+        return $"|     |{BuildTimeSpan(ElapsedTime)}|           |             ";
     }
 
     protected override string GetEventMessage(Trace2FormatTarget formatTarget)
@@ -318,6 +320,8 @@ public class ChildExitMessage : Trace2Message
     public int Code { get; set; }
 
     [JsonProperty("t_rel")]
+    public double RelativeTime { get; set; }
+
     public double ElapsedTime { get; set; }
 
     public override string ToJson()
@@ -342,7 +346,7 @@ public override string ToPerformanceString()
 
     protected override string BuildPerformanceSpan()
     {
-        return $"|     |{BuildTimeSpan(ElapsedTime)}|           |             ";
+        return $"|     |{BuildTimeSpan(ElapsedTime)}|{BuildTimeSpan(RelativeTime)}|             ";
     }
 
     protected override string GetEventMessage(Trace2FormatTarget formatTarget)
@@ -354,7 +358,7 @@ protected override string GetEventMessage(Trace2FormatTarget formatTarget)
         else
             sb.Append($"[{Id}]");
 
-        sb.Append($" pid:{Pid} code:{Code} elapsed:{ElapsedTime}");
+        sb.Append($" pid:{Pid} code:{Code} elapsed:{RelativeTime}");
         return sb.ToString();
     }
 }

src/shared/TestInfrastructure/Objects/NullTrace.cs

@@ -72,7 +72,7 @@ public void WriteChildStart(DateTimeOffset startTime,
             int lineNumber = 0) { }
 
         public void WriteChildExit(
-            double elapsedTime,
+            double relativeTime,
             int pid,
             int code,
             string filePath = "",