Replace try/finally with PerformanceTag.makeCurrentWhile().

pkg/analysis_server/lib/src/channel/web_socket_channel.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 channel.web_socket;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/channel/channel.dart';
 import 'package:analysis_server/src/protocol.dart';
 import 'package:analyzer/instrumentation/instrumentation.dart';
-import 'package:analyzer/src/generated/utilities_general.dart';
 
 
 /**
  * Instances of the class [WebSocketClientChannel] implement a
  * [ClientCommunicationChannel] that uses a [WebSocket] to communicate with
  * servers.
  */
 class WebSocketClientChannel implements ClientCommunicationChannel {
   /**
    * The socket being wrapped.
@@ skipping 74 matching lines @@
 
   /**
    * Read a request from the given [data] and use the given function to handle
    * the request.
    */
   void readRequest(Object data, void onRequest(Request request)) {
     if (data is String) {
       instrumentationService.logRequest(data);
       // Parse the string as a JSON descriptor and process the resulting
       // structure as a request.
-      PerformanceTag prevTag =
-          ServerPerformanceStatistics.serverChannel.makeCurrent();
-      try {
+      ServerPerformanceStatistics.serverChannel.makeCurrentWhile(() {
         Request request = new Request.fromString(data);
         if (request == null) {
           sendResponse(new Response.invalidRequestFormat());
           return;
         }
         onRequest(request);
-      } finally {
-        prevTag.makeCurrent();
-      }
+      });
     } else if (data is List<int>) {
       // TODO(brianwilkerson) Implement a more efficient protocol.
       sendResponse(new Response.invalidRequestFormat());
     } else {
       sendResponse(new Response.invalidRequestFormat());
     }
   }
 
   @override
   void sendNotification(Notification notification) {
-    PerformanceTag prevTag =
-        ServerPerformanceStatistics.serverChannel.makeCurrent();
-    try {
+    ServerPerformanceStatistics.serverChannel.makeCurrentWhile(() {
       String jsonEncoding = JSON.encode(notification.toJson());
       socket.add(jsonEncoding);
       instrumentationService.logNotification(jsonEncoding);
-    } finally {
-      prevTag.makeCurrent();
-    }
+    });
   }
 
   @override
   void sendResponse(Response response) {
-    PerformanceTag prevTag =
-        ServerPerformanceStatistics.serverChannel.makeCurrent();
-    try {
+    ServerPerformanceStatistics.serverChannel.makeCurrentWhile(() {
       String jsonEncoding = JSON.encode(response.toJson());
       socket.add(jsonEncoding);
       instrumentationService.logResponse(jsonEncoding);
-    } finally {
-      prevTag.makeCurrent();
-    }
+    });
   }
 }