Ensure shutdown is always called

pkg/analyzer/lib/instrumentation/instrumentation.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 instrumentation;
 
 /**
  * The interface used by client code to communicate with an instrumentation
  * server.
  */
@@ skipping 24 matching lines @@
 }
 
 /**
  * The interface used by client code to communicate with an instrumentation
  * server by wrapping an [InstrumentationServer].
  */
 class InstrumentationService {
   /**
    * An instrumentation service that will not log any instrumentation data.
    */
-  static const InstrumentationService NULL_SERVICE =
-      const InstrumentationService(null);
+  static final InstrumentationService NULL_SERVICE =
+      new InstrumentationService(null);
 
   static const String TAG_NOTIFICATION = 'Noti';
   static const String TAG_REQUEST = 'Req';
   static const String TAG_RESPONSE = 'Res';
   static const String TAG_VERSION = 'Ver';
 
   /**
    * The instrumentation server used to communicate with the server, or `null`
    * if instrumentation data should not be logged.
    */
-  final InstrumentationServer instrumentationServer;
+  InstrumentationServer _instrumentationServer;
 
   /**
    * Initialize a newly created instrumentation service to comunicate with the
    * given [instrumentationServer].
    */
-  const InstrumentationService(this.instrumentationServer);
+  InstrumentationService(this._instrumentationServer);
 
   /**
    * The current time, expressed as a decimal encoded number of milliseconds.
    */
   String get _timestamp => new DateTime.now().millisecond.toString();
 
   /**
    * Log that a notification has been sent to the client.
    */
   void logNotification(String notification) {
@@ skipping 13 matching lines @@
   void logResponse(String response) {
     _log(TAG_RESPONSE, response);
   }
 
   /**
    * Signal that the client is done communicating with the instrumentation
    * server. This method should be invoked exactly one time and no other methods
    * should be invoked on this instance after this method has been invoked.
    */
   void shutdown() {
-    if (instrumentationServer != null) {
-      instrumentationServer.shutdown();
+    if (_instrumentationServer != null) {
+      _instrumentationServer.shutdown();
+      _instrumentationServer = null;
     }
   }
 
   /**
    * Log the given message with the given tag.
    */
   void _log(String tag, String message) {
-    if (instrumentationServer != null) {
-      instrumentationServer.log('$_timestamp:$tag:$message');
+    if (_instrumentationServer != null) {
+      _instrumentationServer.log('$_timestamp:$tag:$message');
     }
   }
 }