Preserve marking bits across scavenges if incremental marker is running.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index c91f2ab8d81e6da376a1712694727f063f89cef1..fa1c34d45f186873990e7992e4e52d72e3a57591 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -1473,6 +1473,8 @@ class Heap : public AllStatic {
     return high_survival_rate_period_length_ > 0;
   }
 
+  static void SelectScavengingVisitorsTable();
+
   static const int kInitialSymbolTableSize = 2048;
   static const int kInitialEvalCacheSize = 64;
 
@@ -1791,6 +1793,10 @@ class MarkingStack {
     return object;
   }
 
+  HeapObject** low() { return low_; }
+  HeapObject** top() { return top_; }
+  void set_top(HeapObject** top) { top_ = top; }
+
  private:
   HeapObject** low_;
   HeapObject** top_;