Handle HostedRunnerShutdownMessage from service to shutdown hosted runner faster. (#1922)

src/Sdk/DTPipelines/Pipelines/RunnerShutdownMessage.cs

@@ -0,0 +1,39 @@
+using System;
+using System.Runtime.Serialization;
+using GitHub.Services.WebApi;
+using Newtonsoft.Json;
+
+namespace GitHub.DistributedTask.Pipelines
+{
+    [DataContract]
+    public sealed class HostedRunnerShutdownMessage
+    {
+        public static readonly String MessageType = "RunnerShutdown";
+
+        [JsonConstructor]
+        internal HostedRunnerShutdownMessage()
+        {
+        }
+
+        public HostedRunnerShutdownMessage(String reason)
+        {
+            this.Reason = reason;
+        }
+
+        [DataMember]
+        public String Reason
+        {
+            get;
+            private set;
+        }
+
+        public WebApi.TaskAgentMessage GetAgentMessage()
+        {
+            return new WebApi.TaskAgentMessage
+            {
+                Body = JsonUtility.ToString(this),
+                MessageType = HostedRunnerShutdownMessage.MessageType,
+            };
+        }
+    }
+}