improve completion performance status page

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

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library services.completion.computer;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol.dart';
 import 'package:analysis_server/src/services/completion/dart_completion_manager.dart';
@@ skipping 97 matching lines @@
       });
     });
     return controller.stream;
   }
 }
 
 /**
  * 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>[];
 
   Source source;
   int offset;
   String contents;
   int notificationCount = -1;
   int suggestionCount = -1;
+  Duration _firstNotification;
 
   CompletionPerformance() {
     _stopwatch.start();
   }
 
   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 '???';
     }
     int start = offset;
     while (start > 0) {
       String ch = contents[start - 1];
       if (ch == '\r' || ch == '\n') {
         break;
       }
@@ skipping 29 matching lines @@
       }
     } else {
       result = f();
       start = end;
       end = _stopwatch.elapsed;
     }
     _logDuration(tag, end - start);
     return result;
   }
 
+  void logFirstNotificationComplete(String tag) {
+    _firstNotification = _stopwatch.elapsed;
+    _logDuration(tag, _firstNotification);
+  }
+
   void logStartTime(String tag) {
     _startTimes[tag] = _stopwatch.elapsed;
   }
 
   void _logDuration(String tag, Duration elapsed) {
     operations.add(new OperationPerformance(tag, elapsed));
   }
 }
 
 /**
@@ skipping 68 matching lines @@
    */
   final String name;
 
   /**
    * The elapse time or `null` if undefined.
    */
   final Duration elapsed;
 
   OperationPerformance(this.name, this.elapsed);
 }