[heap] Fix live object iterator to skip grey filler objects.

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 177 matching lines @@
           }
 
           // Clear all bits in current_cell, including the end index.
           current_cell_ &= ~(end_index_mask + end_index_mask - 1);
         }
 
         if (T == kBlackObjects || T == kAllLiveObjects) {
           object = black_object;
         }
       } else if ((T == kGreyObjects || T == kAllLiveObjects)) {
+        map = base::NoBarrierAtomicValue<Map*>::FromAddress(addr)->Value();
         object = HeapObject::FromAddress(addr);
       }
 
       // We found a live object.
       if (object != nullptr) {
-        if (map != nullptr && map == heap()->one_pointer_filler_map()) {
+        if (map == heap()->one_pointer_filler_map()) {
           // Black areas together with slack tracking may result in black one
           // word filler objects. We filter these objects out in the iterator.
           object = nullptr;
         } else {
           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_