Add RDT count to the analysis_complete event (microsoft#1396)

* Add RDT count to the analysis_complete event

* Use property instead of method

Author: jakebailey

src/Analysis/Ast/Impl/Documents/Definitions/IRunningDocumentTable.cs

@@ -90,5 +90,10 @@ public interface IRunningDocumentTable {
         /// Fires when document is removed.
         /// </summary>
         event EventHandler<DocumentEventArgs> Removed;
+
+        /// <summary>
+        /// Gets the number of documents in the table.
+        /// </summary>
+        int DocumentCount { get; }
     }
 }

src/Analysis/Ast/Impl/Documents/RunningDocumentTable.cs

@@ -69,6 +69,14 @@ public IEnumerable<IDocument> GetDocuments() {
             }
         }
 
+        public int DocumentCount {
+            get {
+                lock (_lock) {
+                    return _documentsByUri.Count;
+                }
+            }
+        }
+
         /// <summary>
         /// Adds file to the list of available documents.
         /// </summary>

src/LanguageServer/Impl/Implementation/Server.Telemetry.cs

@@ -48,6 +48,7 @@ private void OnAnalysisComplete(object sender, AnalysisCompleteEventArgs e) {
             te.Measurements["workingMB"] = workingMB;
             te.Measurements["elapsedMs"] = e.MillisecondsElapsed;
             te.Measurements["moduleCount"] = e.ModuleCount;
+            te.Measurements["rdtCount"] = _rdt.DocumentCount;
 
             telemetry.SendTelemetryAsync(te).DoNotWait();
         }