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

runtime/vm/kernel_reader.cc

Index: runtime/vm/kernel_reader.cc
diff --git a/runtime/vm/kernel_reader.cc b/runtime/vm/kernel_reader.cc
index 1ddd641c9155bb545659bbdd721b26338da307e9..583d7db52dae3d2d369315a838d91570d05a113d 100644
--- a/runtime/vm/kernel_reader.cc
+++ b/runtime/vm/kernel_reader.cc
@@ -176,50 +176,18 @@ Object& KernelReader::ReadProgram() {
     }
 
     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());
-
-      Function& to_patch = Function::Handle(
-          Z, builtin_library.LookupFunctionAllowPrivate(
-                 dart::String::Handle(dart::String::New("_getMainClosure"))));
-
-      Procedure* procedure =
-          reinterpret_cast<Procedure*>(to_patch.kernel_function());
-      // If dart:_builtin was not compiled from Kernel at all it does not need
-      // to be patched.
-      if (procedure != NULL) {
-        // We will handle the StaticGet specially and will not use the name.
-        // Note that we pass "true" in cannot_stream to avoid trying to stream
-        // a non-existing part of the binary.
-        //
-        // TODO(kmillikin): we are leaking the new function body.  Find a way to
-        // deallocate it.
-        procedure->function()->ReplaceBody(
-            new ReturnStatement(new StaticGet(NameIndex(), false), false));
-      }
+      ASSERT(library.LookupObjectAllowPrivate(H.DartSymbol("main")) !=
+             Object::null());
       return library;
     }
   }