completion performance measurement for local status page

pkg/analysis_server/lib/src/services/completion/completion_performance.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.manager;
 
 import 'package:analyzer/src/generated/source.dart';
 
 /**
  * Overall performance of a code completion operation.
@@ skipping 27 matching lines @@
     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);
   }
 
-  logElapseTime(String tag, [f() = null]) {
-    Duration start;
+  void logElapseTime(String tag) {
     Duration end = _stopwatch.elapsed;
-    var result;
-    if (f == null) {
-      start = _startTimes[tag];
-      if (start == null) {
-        _logDuration(tag, null);
-        return null;
-      }
-    } else {
-      result = f();
-      start = end;
-      end = _stopwatch.elapsed;
+    Duration start = _startTimes[tag];
+    if (start == null) {
+      _logDuration(tag, null);
+      return null;
     }
     _logDuration(tag, end - start);
-    return result;
   }
 
   void logFirstNotificationComplete(String tag) {
     _firstNotification = _stopwatch.elapsed;
     _logDuration(tag, _firstNotification);
   }
 
   void logStartTime(String tag) {
     _startTimes[tag] = _stopwatch.elapsed;
   }
@@ skipping 44 matching lines @@
    */
   final String name;
 
   /**
    * The elapse time or `null` if undefined.
    */
   final Duration elapsed;
 
   OperationPerformance(this.name, this.elapsed);
 }