[heap] Implement simple marking in the concurrent marking thread.

test/cctest/heap/test-concurrent-marking.cc

 // Copyright 2017 the V8 project authors. 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 "src/v8.h"
 
 #include "src/heap/concurrent-marking.h"
 #include "src/heap/heap-inl.h"
 #include "src/heap/heap.h"
 #include "test/cctest/cctest.h"
 #include "test/cctest/heap/heap-utils.h"
 
 namespace v8 {
 namespace internal {
 TEST(ConcurrentMarking) {
   i::FLAG_concurrent_marking = true;
   CcTest::InitializeVM();
   Heap* heap = CcTest::heap();
   ConcurrentMarking* concurrent_marking = new ConcurrentMarking(heap);
-  for (int i = 0; i < 10; i++) {
-    concurrent_marking->EnqueueObject(heap->undefined_value());
-  }
-  concurrent_marking->StartMarkingTasks(3);
-  while (!concurrent_marking->IsQueueEmpty()) {
-  }
-  concurrent_marking->WaitForTasksToComplete();
+  concurrent_marking->AddRoot(heap->undefined_value());
+  concurrent_marking->StartMarkingTask();
+  concurrent_marking->WaitForTaskToComplete();
   delete concurrent_marking;
 }
 
 }  // namespace internal
 }  // namespace v8