[heap] Do not clear second bit when iterating for grey objects on black pages.

src/heap/mark-compact-inl.h

 // 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.
 
 #ifndef V8_HEAP_MARK_COMPACT_INL_H_
 #define V8_HEAP_MARK_COMPACT_INL_H_
 
 #include "src/heap/mark-compact.h"
 #include "src/heap/remembered-set.h"
 #include "src/isolate.h"
@@ skipping 164 matching lines @@
       }
       if (T == kBlackObjects && (current_cell_ & second_bit_index)) {
         object = HeapObject::FromAddress(addr);
       } else if (T == kGreyObjects && !(current_cell_ & second_bit_index)) {
         object = HeapObject::FromAddress(addr);
       } else if (T == kAllLiveObjects) {
         object = HeapObject::FromAddress(addr);
       } else if (T == kGreyObjectsOnBlackPage) {
         object = HeapObject::FromAddress(addr);
       }
-      // Clear the second bit of the found object.
-      current_cell_ &= ~second_bit_index;
+
+      if (T != kGreyObjectsOnBlackPage) {
+        // Clear the second bit of the found object.
+        current_cell_ &= ~second_bit_index;
+      }
 
       // We found a live object.
       if (object != nullptr) break;
     }
     if (current_cell_ == 0) {
       if (!it_.Done()) {
         it_.Advance();
         cell_base_ = it_.CurrentCellBase();
         current_cell_ = *it_.CurrentCell();
       }
     }
     if (object != nullptr) return object;
   }
   return nullptr;
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_MARK_COMPACT_INL_H_