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 d6f10e601326f92dbf716735b1a69fc8e9a5eea9..aa3df2de77529a59beac81a2ec0d711b39893471 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -159,15 +159,21 @@ class Marking : public AllStatic {
 
   // Returns true if the transferred color is black.

[Hannes Payer (out of office), 2016/05/20 07:34:41]

Mention that this function clears the color of the source object.

[Marcel Hlopko, 2016/05/20 14:31:41]

Done.

   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;
       }
     }