enable analysis server cmdline instrumentation log file option

pkg/analysis_server/lib/src/server/driver.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 driver;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:math';
 
@@ skipping 363 matching lines @@
     if (results[SDK_OPTION] != null) {
       defaultSdk = new DirectoryBasedDartSdk(new JavaFile(results[SDK_OPTION]));
     } else {
       // No path to the SDK provided; use DirectoryBasedDartSdk.defaultSdk,
       // which will make a guess.
       defaultSdk = DirectoryBasedDartSdk.defaultSdk;
     }
     //
     // Initialize the instrumentation service.
     //
-    if (instrumentationServer != null) {
-      String filePath = results[INSTRUMENTATION_LOG_FILE];
-      if (filePath != null) {
-        instrumentationServer = new MulticastInstrumentationServer(
-            [instrumentationServer, new FileInstrumentationServer(filePath)]);
-      }
+    String logFilePath = results[INSTRUMENTATION_LOG_FILE];
+    if (logFilePath != null) {
+      FileInstrumentationServer fileBasedServer =
+          new FileInstrumentationServer(logFilePath);
+      instrumentationServer = instrumentationServer != null
+          ? new MulticastInstrumentationServer(
+              [instrumentationServer, fileBasedServer])
+          : fileBasedServer;
     }
     InstrumentationService service =
         new InstrumentationService(instrumentationServer);
     service.logVersion(_readUuid(service), results[CLIENT_ID],
         results[CLIENT_VERSION], AnalysisServer.VERSION, defaultSdk.sdkVersion);
     AnalysisEngine.instance.instrumentationService = service;
     //
     // Enable the new task model, if appropriate.
     //
     AnalysisEngine.instance.useTaskModel = !results[DISABLE_NEW_TASK_MODEL];
@@ skipping 168 matching lines @@
       uuidFile.parent.createSync(recursive: true);
       uuidFile.writeAsStringSync(uuid);
     } catch (exception, stackTrace) {
       service.logPriorityException(exception, stackTrace);
       // Slightly alter the uuid to indicate it was not persisted
       uuid = 'temp-$uuid';
     }
     return uuid;
   }
 }