Fix build

sdk/lib/developer/timeline.dart

 // Copyright (c) 2015, 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.
 
 part of dart.developer;
 
 typedef dynamic TimelineSyncFunction();
 
 /// Add to the timeline.
 class Timeline {
@@ skipping 117 matching lines @@
   final int _taskId;
   /// An (optional) set of arguments which will be serialized to JSON and
   /// associated with this block.
   final Map arguments = {};
   bool _finished = false;
 
   AsyncBlock._(this.name, this._taskId, this.category);
 
   // Emit the start event.
   void _start() {
-    arguments['isolateNumber'] = Timeline._isolateId;
+    arguments['isolateNumber'] = '${Timeline._isolateId}';
     String argumentsAsJson = JSON.encode(arguments);
     _reportTaskEvent(_getTraceClock(),
                      _taskId,
                      'b',
                      category,
                      name,
                      argumentsAsJson);
   }
 
   // Emit the finish event.
@@ skipping 44 matching lines @@
   final int _start;
 
   _SyncBlock._(this.name,
                this._start);
 
   /// Finish this block of time. At this point, this block can no longer be
   /// used.
   void finish() {
     var end = _getTraceClock();
 
-    arguments['isolateNumber'] = Timeline._isolateId;
+    arguments['isolateNumber'] = '${Timeline._isolateId}';
 
     // Encode arguments map as JSON before reporting.
     var argumentsAsJson = JSON.encode(arguments);
 
     // Report event to runtime.
     _reportCompleteEvent(_start,
                          end,
                          category,
                          name,
                          argumentsAsJson);
@@ skipping 16 matching lines @@
                                String category,
                                String name,
                                String argumentsAsJson);
 
 /// Reports a complete synchronous event.
 external void _reportCompleteEvent(int start,
                                    int end,
                                    String category,
                                    String name,
                                    String argumentsAsJson);