1. Dynamic compute the main closure that needs to be run by the main isolate

runtime/vm/kernel_reader.cc

 // 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.
 
 #include "vm/kernel_reader.h"
 
 #include <string.h>
 
 #include "vm/dart_api_impl.h"
 #include "vm/kernel_binary.h"
@@ skipping 158 matching lines @@
       ReadLibrary(kernel_library);
     }
 
     for (intptr_t i = 0; i < length; i++) {
       dart::Library& library =
           LookupLibrary(program_->libraries()[i]->canonical_name());
       if (!library.Loaded()) library.SetLoaded();
     }
 
     if (ClassFinalizer::ProcessPendingClasses(/*from_kernel=*/true)) {
-      // There is a function _getMainClosure in dart:_builtin that returns the
-      // main procedure.  Since the platform libraries are compiled before the
-      // program script, this function might need to be patched here.
-
-      // If there is no main method then we have compiled a partial Kernel file
-      // and do not need to patch here.
+      // If 'main' is not found return a null library, this is the case
+      // when bootstrapping is in progress.
       NameIndex main = program_->main_method();
       if (main == -1) {
         return dart::Library::Handle(Z);
       }
 
-      // If the builtin library is not set in the object store, then we are
-      // bootstrapping and do not need to patch here.
-      dart::Library& builtin_library =
-          dart::Library::Handle(Z, I->object_store()->builtin_library());
-      if (builtin_library.IsNull()) {
-        return dart::Library::Handle(Z);
-      }
-
       NameIndex main_library = H.EnclosingName(main);
       dart::Library& library = LookupLibrary(main_library);
       // Sanity check that we can find the main entrypoint.
-      Object& main_obj = Object::Handle(
-          Z, library.LookupObjectAllowPrivate(H.DartSymbol("main")));
-      ASSERT(!main_obj.IsNull());
-
+      ASSERT(library.LookupObjectAllowPrivate(H.DartSymbol("main")) !=
+             Object::null());
       return library;
     }
   }
 
   // Either class finalization failed or we caught a compile error.
   // In both cases sticky error would be set.
   Error& error = Error::Handle(Z);
   error = thread_->sticky_error();
   thread_->clear_sticky_error();
   return error;
@@ skipping 705 matching lines @@
   initializer_fun.set_is_debuggable(false);
   initializer_fun.set_is_reflectable(false);
   initializer_fun.set_is_inlinable(false);
   return new (zone) ParsedFunction(thread, initializer_fun);
 }
 
 
 }  // namespace kernel
 }  // namespace dart
 #endif  // !defined(DART_PRECOMPILED_RUNTIME)