MarkBit cleanup: They have to be accessed through Marking accessors.

src/heap/heap.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/v8.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/base/bits.h"
 #include "src/base/once.h"
@@ skipping 5778 matching lines @@
   explicit UnreachableObjectsFilter(Heap* heap) : heap_(heap) {
     MarkReachableObjects();
   }
 
   ~UnreachableObjectsFilter() {
     heap_->mark_compact_collector()->ClearMarkbits();
   }
 
   bool SkipObject(HeapObject* object) {
     MarkBit mark_bit = Marking::MarkBitFrom(object);
-    return !mark_bit.Get();
+    return Marking::IsWhite(mark_bit);
   }
 
  private:
   class MarkingVisitor : public ObjectVisitor {
    public:
     MarkingVisitor() : marking_stack_(10) {}
 
     void VisitPointers(Object** start, Object** end) {
       for (Object** p = start; p < end; p++) {
         if (!(*p)->IsHeapObject()) continue;
         HeapObject* obj = HeapObject::cast(*p);
         MarkBit mark_bit = Marking::MarkBitFrom(obj);
-        if (!mark_bit.Get()) {
-          mark_bit.Set();
+        if (Marking::IsWhite(mark_bit)) {
+          Marking::WhiteToBlack(mark_bit);
           marking_stack_.Add(obj);
         }
       }
     }
 
     void TransitiveClosure() {
       while (!marking_stack_.is_empty()) {
         HeapObject* obj = marking_stack_.RemoveLast();
         obj->Iterate(this);
       }
@@ skipping 566 matching lines @@
       static_cast<int>(object_sizes_last_time_[index]));
   CODE_AGE_LIST_COMPLETE(ADJUST_LAST_TIME_OBJECT_COUNT)
 #undef ADJUST_LAST_TIME_OBJECT_COUNT
 
   MemCopy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   MemCopy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 }
 }  // namespace v8::internal