Preserve marking bits across scavenges if incremental marker is running.

src/incremental-marking.h

Index: src/incremental-marking.h
diff --git a/src/incremental-marking.h b/src/incremental-marking.h
index 98a87e0bd83f5b9c9d157ab34a89e4c92a101833..122f53771488084e3b847a929ea70f6d05455017 100644
--- a/src/incremental-marking.h
+++ b/src/incremental-marking.h
@@ -58,6 +58,10 @@ class IncrementalMarking : public AllStatic {
 
   static void Stop();
 
+  static void PrepareForScavenge();
+
+  static void UpdateMarkingStackAfterScavenge();
+
   static void Hurry();
 
   static void Finalize();
@@ -160,6 +164,16 @@ class IncrementalMarking : public AllStatic {
     ASSERT(!marking_stack_.overflowed());
   }
 
+  static inline void MarkWhiteObjectGrey(HeapObject* obj, MarkBit mark_bit) {
+    ASSERT(Marking::MarkBitFrom(obj) == mark_bit);
+    ASSERT(obj->Size() >= 2*kPointerSize);
+    ASSERT(!IsStopped());
+    ASSERT(IsWhite(mark_bit));
+    mark_bit.Set();
+    mark_bit.Next().Set();
+    ASSERT(IsGrey(mark_bit));
+  }
+
   static inline void MarkBlack(MarkBit mark_bit) {
     mark_bit.Set();
     mark_bit.Next().Clear();
@@ -174,6 +188,22 @@ class IncrementalMarking : public AllStatic {
     return "???";
   }
 
+  enum ObjectColor {
+    BLACK_OBJECT,
+    WHITE_OBJECT,
+    GREY_OBJECT,
+    IMPOSSIBLE_COLOR
+  };
+
+  static inline ObjectColor Color(HeapObject* obj) {
+    MarkBit mark_bit = Marking::MarkBitFrom(obj);
+    if (IsBlack(mark_bit)) return BLACK_OBJECT;
+    if (IsWhite(mark_bit)) return WHITE_OBJECT;
+    if (IsGrey(mark_bit)) return GREY_OBJECT;
+    UNREACHABLE();
+    return IMPOSSIBLE_COLOR;
+  }
+
  private:
   static State state_;
   static MarkingStack marking_stack_;