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

runtime/bin/main.cc

 // Copyright (c) 2012, 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.
 
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
 
 #include "include/dart_api.h"
 #include "include/dart_tools_api.h"
@@ skipping 1817 matching lines @@
 
 #if !defined(PRODUCT) && !defined(DART_PRECOMPILED_RUNTIME)
   // Constant true if PRODUCT or DART_PRECOMPILED_RUNTIME.
   if ((gen_snapshot_kind != kNone) || run_app_snapshot) {
     vm_options.AddArgument("--load_deferred_eagerly");
   }
 #endif
 
   if (gen_snapshot_kind == kAppJIT) {
     vm_options.AddArgument("--fields_may_be_reset");
+    vm_options.AddArgument("--collect_code=false");
   }
   if ((gen_snapshot_kind == kAppAOT) || is_noopt) {
     vm_options.AddArgument("--precompilation");
   }
 #if defined(DART_PRECOMPILED_RUNTIME)
   vm_options.AddArgument("--precompilation");
 #endif
   if (gen_snapshot_kind == kAppJIT) {
     Process::SetExitHook(SnapshotOnExitHook);
   }
@@ skipping 70 matching lines @@
   Platform::Exit(Process::GlobalExitCode());
 }
 
 }  // namespace bin
 }  // namespace dart
 
 int main(int argc, char** argv) {
   dart::bin::main(argc, argv);
   UNREACHABLE();
 }