Added parallel marking threads.

src/mark-compact.h

Index: src/mark-compact.h
diff --git a/src/mark-compact.h b/src/mark-compact.h
index 0c98016fd2b2246470752fa30d857e3525aac7eb..9cdb46a4f9df60b35845117c020ec604f61555b6 100644
--- a/src/mark-compact.h
+++ b/src/mark-compact.h
@@ -680,6 +680,7 @@ class MarkCompactCollector {
 
   MarkingParity marking_parity() { return marking_parity_; }
 
+  // Concurrent and parallel sweeping support.
   void SweepInParallel(PagedSpace* space,
                        FreeList* private_free_list,
                        FreeList* free_list);
@@ -690,6 +691,11 @@ class MarkCompactCollector {
 
   bool AreSweeperThreadsActivated();
 
+  // Parallel marking support.
+  void MarkInParallel();
+
+  void WaitUntilMarkingCompleted();
+
  private:
   MarkCompactCollector();
   ~MarkCompactCollector();