Add flag to control background finalization.

runtime/vm/dart_api_state.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/dart_api_state.h"
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/heap.h"
 #include "vm/isolate.h"
 #include "vm/lockers.h"
 #include "vm/thread.h"
 #include "vm/timeline.h"
 
 namespace dart {
 
 BackgroundFinalizer::BackgroundFinalizer(Isolate* isolate,
                                          FinalizationQueue* queue) :
     isolate_(isolate),
     queue_(queue) {
+  ASSERT(FLAG_background_finalization);
   MonitorLocker ml(isolate->heap()->finalization_tasks_lock());
   isolate->heap()->set_finalization_tasks(
       isolate->heap()->finalization_tasks() + 1);
   ml.Notify();
 }
 
 
 void BackgroundFinalizer::Run() {
   bool result = Thread::EnterIsolateAsHelper(isolate_,
                                              Thread::kFinalizerTask);
@@ skipping 15 matching lines @@
 
   {
     Heap* heap = isolate_->heap();
     MonitorLocker ml(heap->finalization_tasks_lock());
     heap->set_finalization_tasks(heap->finalization_tasks() - 1);
     ml.Notify();
   }
 }
 
 }  // namespace dart