Ensure black and gray objects are kept around by scavenger

src/heap/mark-compact.h

Index: src/heap/mark-compact.h
diff --git a/src/heap/mark-compact.h b/src/heap/mark-compact.h
index d6adb038ea95764286f3a24bcdfb3003050ec7ec..c9e867e1f4eac39e1cfd6c959c6ab3ffdc8956e8 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -157,17 +157,24 @@ class Marking : public AllStatic {
   }
 #endif
 
-  // Returns true if the transferred color is black.
+  // Returns true if the transferred color is black. Clears the color of the
+  // from object.
   INLINE(static bool TransferColor(HeapObject* from, HeapObject* to)) {
-    if (Page::FromAddress(to->address())->IsFlagSet(Page::BLACK_PAGE))
-      return true;
     MarkBit from_mark_bit = MarkBitFrom(from);
+    if (Page::FromAddress(to->address())->IsFlagSet(Page::BLACK_PAGE)) {
+      if (!Marking::IsWhite(from_mark_bit)) {
+        Marking::MarkWhite(from_mark_bit);
+      }
+      return true;
+    }
     MarkBit to_mark_bit = MarkBitFrom(to);
     DCHECK(Marking::IsWhite(to_mark_bit));
     if (from_mark_bit.Get()) {
       to_mark_bit.Set();
+      from_mark_bit.Clear();
       if (from_mark_bit.Next().Get()) {
         to_mark_bit.Next().Set();
+        from_mark_bit.Next().Clear();
         return true;
       }
     }