When building app snapshots for the SDK, train dart2js on itself.

utils/compiler/BUILD.gn

 # Copyright (c) 2016, 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("//build/compiled_action.gni")
 import("../create_timestamp.gni")
 import("../application_snapshot.gni")
 
 create_timestamp_file("dart2js_files_stamp") {
   path = rebase_path("../../pkg/compiler/lib")
@@ skipping 44 matching lines @@
   ]
 }
 
 application_snapshot("dart2js") {
   deps = [
     ":dart2js_create_snapshot_entries",
   ]
   main_dart = "$root_gen_dir/dart2js.dart"
   training_args = [
     "--library-root=" + rebase_path("../../sdk"),
-    rebase_path("../../tests/language/first_test.dart"),
+    "--categories=all",
+    rebase_path("$root_gen_dir/dart2js.dart"),
   ]
 }
 
 application_snapshot("utils_wrapper") {
   deps = [
     ":dart2js_create_snapshot_entries",
   ]
   main_dart = "$root_gen_dir/utils_wrapper.dart"
   training_args = [ "--help" ]
 }