Ensure that there is a stack trace when reporting a server error

pkg/analysis_server/lib/src/analysis_server.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 analysis.server;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:core' hide Resource;
 import 'dart:math' show max;
@@ skipping 849 matching lines @@
     if (exception != null) {
       exceptionString = exception.toString();
     } else {
       exceptionString = 'null exception';
     }
     // prepare stackTrace.toString()
     String stackTraceString;
     if (stackTrace != null) {
       stackTraceString = stackTrace.toString();
     } else {
-      stackTraceString = 'null stackTrace';
+      try {
+        throw 'ignored';
+      } catch (ignored, stackTrace) {
+        stackTraceString = stackTrace.toString();
+      }
+      if (stackTraceString == null) {
+        // This code should be unreachable.
+        stackTraceString = 'null stackTrace';
+      }
     }
     // send the notification
     channel.sendNotification(
         new ServerErrorParams(fatal, exceptionString, stackTraceString)
             .toNotification());
   }
 
   /**
    * Send status notification to the client. The `operation` is the operation
    * being performed or `null` if analysis is complete.
@@ skipping 684 matching lines @@
   /**
    * The [PerformanceTag] for time spent in server request handlers.
    */
   static PerformanceTag serverRequests = new PerformanceTag('serverRequests');
 
   /**
    * The [PerformanceTag] for time spent in split store microtasks.
    */
   static PerformanceTag splitStore = new PerformanceTag('splitStore');
 }