Introduce --zap-cpp-pointers (off by default)

src/heap/spaces.cc

 // Copyright 2011 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/spaces.h"
 
 #include <utility>
 
 #include "src/base/bits.h"
 #include "src/base/platform/platform.h"
@@ skipping 3116 matching lines @@
   if (Heap::ShouldZapGarbage()) {
     // Make the object consistent so the heap can be verified in OldSpaceStep.
     // We only need to do this in debug builds or if verify_heap is on.
     reinterpret_cast<Object**>(object->address())[0] =
         heap()->fixed_array_map();
     reinterpret_cast<Object**>(object->address())[1] = Smi::kZero;
   }
 
   heap()->StartIncrementalMarkingIfAllocationLimitIsReached(Heap::kNoGCFlags,
                                                             kNoGCCallbackFlags);
+
   AllocationStep(object->address(), object_size);
 
   heap()->CreateFillerObjectAt(object->address(), object_size,
                                ClearRecordedSlots::kNo);
 
   if (heap()->incremental_marking()->black_allocation()) {
     ObjectMarking::WhiteToBlack(object, MarkingState::Internal(object));
   }
   return object;
 }
@@ skipping 236 matching lines @@
     PrintF("\n");
   }
   printf(" --------------------------------------\n");
   printf(" Marked: %x, LiveCount: %" V8PRIdPTR "\n", mark_size,
          MarkingState::Internal(this).live_bytes());
 }
 
 #endif  // DEBUG
 }  // namespace internal
 }  // namespace v8