[heap] Iterate handles with special left-trim visitor

src/heap/heap.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_HEAP_H_
 #define V8_HEAP_HEAP_H_
 
 #include <cmath>
 #include <map>
 
@@ skipping 614 matching lines @@
   static double HeapGrowingFactor(double gc_speed, double mutator_speed);
 
   // Copy block of memory from src to dst. Size of block should be aligned
   // by pointer size.
   static inline void CopyBlock(Address dst, Address src, int byte_size);
 
   // Determines a static visitor id based on the given {map} that can then be
   // stored on the map to facilitate fast dispatch for {StaticVisitorBase}.
   static int GetStaticVisitorIdForMap(Map* map);
 
-  // We cannot avoid stale handles to left-trimmed objects, but can only make
-  // sure all handles still needed are updated. Filter out a stale pointer
-  // and clear the slot to allow post processing of handles (needed because
-  // the sweeper might actually free the underlying page).
-  inline bool PurgeLeftTrimmedObject(Object** object);
-
   // Notifies the heap that is ok to start marking or other activities that
   // should not happen during deserialization.
   void NotifyDeserializationComplete();
 
   intptr_t old_generation_allocation_limit() const {
     return old_generation_allocation_limit_;
   }
 
   bool always_allocate() { return always_allocate_scope_count_.Value() != 0; }
 
@@ skipping 2047 matching lines @@
   friend class LargeObjectSpace;
   friend class NewSpace;
   friend class PagedSpace;
   DISALLOW_COPY_AND_ASSIGN(AllocationObserver);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_HEAP_H_