Copy dart2js source into pkg/compiler

pkg/compiler/samples/jsonify/jsonify.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.
 
 import 'dart:io';
 import 'dart:convert';
 
 import 'dart:mirrors';
 
 import '../../../libraries.dart'
@@ skipping 81 matching lines @@
 // This file is generated by jsonify.dart.
 
 library dart.sdk_sources;
 
 const Map<String, String> SDK_SOURCES = const <String, String>''');
     output.writeStringSync(JSON.encode(map).replaceAll(r'$', r'\$'));
     output.writeStringSync(';\n');
   }
   output.closeSync();
 }