improve measurement of completion performance

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 88d1411919cbaa6a48ecdbef5ba4ab45eafc820c..308b8bb4aee590a9d92ef277c6d71149dba0f1e0 100644
--- a/pkg/analysis_server/lib/src/services/completion/completion_manager.dart
+++ b/pkg/analysis_server/lib/src/services/completion/completion_manager.dart
@@ -124,7 +124,8 @@ class CompletionPerformance {
   int offset;
   String contents;
   int notificationCount = -1;
-  int suggestionCount = -1;
+  int suggestionCountFirst = -1;
+  int suggestionCountLast = -1;
   Duration _firstNotification;
 
   CompletionPerformance() {
@@ -162,6 +163,14 @@ class CompletionPerformance {
     return '$prefix^$suffix';
   }
 
+  String get startTimeAndMs => '${start.millisecondsSinceEpoch} - $start';
+
+  String get suggestionCount {
+    if (notificationCount < 1) return '';
+    if (notificationCount == 1) return '$suggestionCountFirst';
+    return '$suggestionCountFirst,  $suggestionCountLast';
+  }
+
   void complete([String tag = null]) {
     _stopwatch.stop();
     _logDuration(tag != null ? tag : 'total time', _stopwatch.elapsed);