dart2js send stats, includes:

pkg/compiler/lib/src/source_file_provider.dart

 // Copyright (c) 2013, 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 source_file_provider;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'dart:math' as math;
@@ skipping 257 matching lines @@
         uri = out;
       } else if (extension == 'precompiled.js') {
         uri = computePrecompiledUri(out);
         onInfo("File ($uri) is compatible with header"
                " \"Content-Security-Policy: script-src 'self'\"");
       } else if (extension == 'js.map' || extension == 'dart.map') {
         uri = sourceMapOut;
       } else if (extension == "info.json") {
         String outName = out.path.substring(out.path.lastIndexOf('/') + 1);
         uri = out.resolve('$outName.$extension');
+      } else if (extension == "stats.json") {
+        String outName = out.path.substring(out.path.lastIndexOf('/') + 1);
+        uri = out.resolve('$outName.$extension');
       } else {
         onFailure('Unknown extension: $extension');
       }
     } else {
       uri = out.resolve('$name.$extension');
     }
 
     if (uri.scheme != 'file') {
       onFailure('Unhandled scheme ${uri.scheme} in $uri.');
     }
@@ skipping 37 matching lines @@
   var onAdd, onClose;
 
   EventSinkWrapper(this.onAdd, this.onClose);
 
   void add(String data) => onAdd(data);
 
   void addError(error, [StackTrace stackTrace]) => throw error;
 
   void close() => onClose();
 }