Fix #419: Log editor IntelliSense duration

Author: daviwil

src/PowerShellEditorServices/Language/AstOperations.cs

@@ -13,6 +13,7 @@
 
 namespace Microsoft.PowerShell.EditorServices
 {
+    using System.Diagnostics;
     using System.Management.Automation;
     using System.Management.Automation.Language;
     using System.Management.Automation.Runspaces;
@@ -101,13 +102,20 @@ static public async Task<CommandCompletion> GetCompletions(
                 {
                     powerShell.Runspace = runspaceHandle.Runspace;
 
+                    Stopwatch stopwatch = new Stopwatch();
+                    stopwatch.Start();
+
                     commandCompletion =
                         CommandCompletion.CompleteInput(
                             scriptAst,
                             currentTokens,
                             cursorPosition,
                             null,
                             powerShell);
+
+                    stopwatch.Stop();
+
+                    Logger.Write(LogLevel.Verbose, $"IntelliSense completed in {stopwatch.ElapsedMilliseconds}ms.");
                 }
             }