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

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

Index: test/cctest/heap/test-concurrent-marking.cc
diff --git a/test/cctest/heap/test-concurrent-marking.cc b/test/cctest/heap/test-concurrent-marking.cc
index 9a50f33f58b3e7eb8c8189d5fbc4b1e0c6f9db7b..ab38efbca55e3aa07857eba71ed539cb3b06968f 100644
--- a/test/cctest/heap/test-concurrent-marking.cc
+++ b/test/cctest/heap/test-concurrent-marking.cc
@@ -19,13 +19,9 @@ TEST(ConcurrentMarking) {
   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;
 }