Add support for building patched_sdk and platform.dill for dart2js:

pkg/front_end/tool/_fasta/generate_dart_libraries.dart

 // Copyright (c) 2017, 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 'package:sdk_library_metadata/libraries.dart'
     show LibraryInfo, libraries;
 
 void main(_) {
   libraries.forEach((String name, LibraryInfo info) {
-    if (info.isVmLibrary) {
-      print('"$name": sdk.resolve("lib/${info.path}"),');
-    }
+    print('"$name": sdk.resolve("lib/${info.path}"),');
   });
 }