Ensure black and gray objects are kept around by scavenger

src/heap/incremental-marking.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/incremental-marking.h"
 
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
 #include "src/conversions.h"
 #include "src/heap/gc-idle-time-handler.h"
@@ skipping 789 matching lines @@
       // entries will not point to forwarding addresses. Hence, we can discard
       // them.
       if (map_word.IsForwardingAddress()) {
         HeapObject* dest = map_word.ToForwardingAddress();
         if (Page::FromAddress(dest->address())->IsFlagSet(Page::BLACK_PAGE))
           continue;
         array[new_top] = dest;
         new_top = ((new_top + 1) & mask);
         DCHECK(new_top != marking_deque->bottom());
 #ifdef DEBUG
+        // Mark bit of the source object should be cleared
         MarkBit mark_bit = Marking::MarkBitFrom(obj);
-        DCHECK(Marking::IsGrey(mark_bit) ||
-               (obj->IsFiller() && Marking::IsWhite(mark_bit)));
+        DCHECK(Marking::IsWhite(mark_bit));
 #endif
       }
     } else if (obj->map() != filler_map) {
       // Skip one word filler objects that appear on the
       // stack when we perform in place array shift.
       array[new_top] = obj;
       new_top = ((new_top + 1) & mask);
       DCHECK(new_top != marking_deque->bottom());
 #ifdef DEBUG
       MarkBit mark_bit = Marking::MarkBitFrom(obj);
@@ skipping 423 matching lines @@
 void IncrementalMarking::IncrementIdleMarkingDelayCounter() {
   idle_marking_delay_counter_++;
 }
 
 
 void IncrementalMarking::ClearIdleMarkingDelayCounter() {
   idle_marking_delay_counter_ = 0;
 }
 }  // namespace internal
 }  // namespace v8