Add support for getting the sessionId from instrumentation and sending it to the client

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 analyzer.instrumentation.instrumentation;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:analyzer/task/model.dart';
 
 /**
  * A container with analysis performance constants.
  */
 class AnalysisPerformanceKind {
   static const String FULL = 'analysis_full';
   static const String INCREMENTAL = 'analysis_incremental';
 }
 
 /**
  * The interface used by client code to communicate with an instrumentation
  * server.
  */
 abstract class InstrumentationServer {
   /**
+   * Return the identifier used to identify the current session.
+   */
+  String get sessionId;
+
+  /**
    * Pass the given [message] to the instrumentation server so that it will be
    * logged with other messages.
    *
    * This method should be used for most logging.
    */
   void log(String message);
 
   /**
    * Pass the given [message] to the instrumentation server so that it will be
    * logged with other messages.
@@ skipping 53 matching lines @@
    */
   InstrumentationService(this._instrumentationServer);
 
   /**
    * Return `true` if this [InstrumentationService] was initialized with a
    * non-`null` server (and hence instrumentation is active).
    */
   bool get isActive => _instrumentationServer != null;
 
   /**
+   * Return the identifier used to identify the current session.
+   */
+  String get sessionId => _instrumentationServer?.sessionId ?? '';
+
+  /**
    * The current time, expressed as a decimal encoded number of milliseconds.
    */
   String get _timestamp => new DateTime.now().millisecondsSinceEpoch.toString();
 
   /**
    * Log that the given analysis [task] is being performed in the given
    * [context].
    */
   void logAnalysisTask(String context, AnalysisTask task) {
     if (_instrumentationServer != null) {
@@ skipping 241 matching lines @@
 
 /**
  * An [InstrumentationServer] that sends messages to multiple instances.
  */
 class MulticastInstrumentationServer implements InstrumentationServer {
   final List<InstrumentationServer> _servers;
 
   MulticastInstrumentationServer(this._servers);
 
   @override
+  String get sessionId => _servers[0].sessionId;
+
+  @override
   void log(String message) {
     for (InstrumentationServer server in _servers) {
       server.log(message);
     }
   }
 
   @override
   void logWithPriority(String message) {
     for (InstrumentationServer server in _servers) {
       server.logWithPriority(message);
     }
   }
 
   @override
   Future shutdown() async {
     for (InstrumentationServer server in _servers) {
       await server.shutdown();
     }
   }
 }