Don't look at timeout value

Under stress scenarios even seeing if the timeout was at least a
specific period of time fails.  Going to a simpler check that we simply
hit the value.

src/Compilers/Server/ServerShared/DiagnosticListener.cs

@@ -26,6 +26,11 @@ internal interface IDiagnosticListener
         /// result.
         /// </summary>
         void DetectedBadConnection();
+
+        /// <summary>
+        /// Called when the server is shutting down because the keep alive timeout was reached.
+        /// </summary>
+        void KeepAliveReached();
     }
 
     internal sealed class EmptyDiagnosticListener : IDiagnosticListener
@@ -41,5 +46,9 @@ public void ConnectionProcessed(int count)
         public void DetectedBadConnection()
         {
         }
+
+        public void KeepAliveReached()
+        {
+        }
     }
 }

src/Compilers/Server/ServerShared/ServerDispatcher.cs

@@ -95,6 +95,7 @@ public void ListenAndDispatchConnections(TimeSpan? keepAlive, CancellationToken
 
                 if ((timeoutTask != null && timeoutTask.IsCompleted) || cancellationToken.IsCancellationRequested)
                 {
+                    _diagnosticListener.KeepAliveReached();
                     listenCancellationTokenSource.Cancel();
                     break;
                 }

src/Compilers/Server/VBCSCompilerTests/CompilerServerApiTest.cs

@@ -22,6 +22,7 @@ private sealed class TestableDiagnosticListener : IDiagnosticListener
             public DateTime? LastProcessedTime;
             public TimeSpan? KeepAlive;
             public bool HasDetectedBadConnection;
+            public bool HitKeepAliveTimeout;
 
             public void ConnectionProcessed(int count)
             {
@@ -38,6 +39,11 @@ public void DetectedBadConnection()
             {
                 HasDetectedBadConnection = true;
             }
+
+            public void KeepAliveReached()
+            {
+                HitKeepAliveTimeout = true;
+            }
         }
 
         private static readonly BuildRequest s_emptyCSharpBuildRequest = new BuildRequest(
@@ -185,11 +191,12 @@ public void KeepAliveNoConnections()
                 .Setup(x => x.CreateListenTask(It.IsAny<CancellationToken>()))
                 .Returns(new TaskCompletionSource<IClientConnection>().Task);
 
-            var dispatcher = new ServerDispatcher(connectionHost.Object, new EmptyDiagnosticListener());
+            var listener = new TestableDiagnosticListener();
+            var dispatcher = new ServerDispatcher(connectionHost.Object, listener);
             var startTime = DateTime.Now;
             dispatcher.ListenAndDispatchConnections(keepAlive);
 
-            Assert.True((DateTime.Now - startTime) > keepAlive);
+            Assert.True(listener.HitKeepAliveTimeout);
         }
 
         /// <summary>
@@ -209,7 +216,7 @@ public void KeepAliveAfterSingleConnection()
 
             Assert.Equal(1, listener.ProcessedCount);
             Assert.True(listener.LastProcessedTime.HasValue);
-            Assert.True((DateTime.Now - listener.LastProcessedTime.Value) > keepAlive);
+            Assert.True(listener.HitKeepAliveTimeout);
         }
 
         /// <summary>
@@ -235,7 +242,7 @@ public void KeepAliveAfterMultipleConnection()
 
             Assert.Equal(count, listener.ProcessedCount);
             Assert.True(listener.LastProcessedTime.HasValue);
-            Assert.True((DateTime.Now - listener.LastProcessedTime.Value) > keepAlive);
+            Assert.True(listener.HitKeepAliveTimeout);
         }
 
         /// <summary>
@@ -282,7 +289,7 @@ public async Task KeepAliveAfterSimultaneousConnection()
             await dispatcherTask.ConfigureAwait(true);
             Assert.Equal(totalCount, listener.ProcessedCount);
             Assert.True(listener.LastProcessedTime.HasValue);
-            Assert.True((DateTime.Now - listener.LastProcessedTime.Value) > keepAlive);
+            Assert.True(listener.HitKeepAliveTimeout);
         }
 
         [Fact]