improve completion performance status page

pkg/analysis_server/lib/src/services/completion/completion_manager.dart

Index: pkg/analysis_server/lib/src/services/completion/completion_manager.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/completion_manager.dart b/pkg/analysis_server/lib/src/services/completion/completion_manager.dart
index a8d16db64cbc37de62bd1182d50e6ff8a9505d78..88d1411919cbaa6a48ecdbef5ba4ab45eafc820c 100644
--- a/pkg/analysis_server/lib/src/services/completion/completion_manager.dart
+++ b/pkg/analysis_server/lib/src/services/completion/completion_manager.dart
@@ -115,6 +115,7 @@ abstract class CompletionManager {
  * Overall performance of a code completion operation.
  */
 class CompletionPerformance {
+  final DateTime start = new DateTime.now();
   final Map<String, Duration> _startTimes = new Map<String, Duration>();
   final Stopwatch _stopwatch = new Stopwatch();
   final List<OperationPerformance> operations = <OperationPerformance>[];
@@ -124,6 +125,7 @@ class CompletionPerformance {
   String contents;
   int notificationCount = -1;
   int suggestionCount = -1;
+  Duration _firstNotification;
 
   CompletionPerformance() {
     _stopwatch.start();
@@ -132,6 +134,9 @@ class CompletionPerformance {
   int get elapsedInMilliseconds =>
       operations.length > 0 ? operations.last.elapsed.inMilliseconds : 0;
 
+  int get firstNotificationInMilliseconds =>
+      _firstNotification != null ? _firstNotification.inMilliseconds : 0;
+
   String get snippet {
     if (contents == null || offset < 0 || contents.length < offset) {
       return '???';
@@ -181,6 +186,11 @@ class CompletionPerformance {
     return result;
   }
 
+  void logFirstNotificationComplete(String tag) {
+    _firstNotification = _stopwatch.elapsed;
+    _logDuration(tag, _firstNotification);
+  }
+
   void logStartTime(String tag) {
     _startTimes[tag] = _stopwatch.elapsed;
   }