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

src/objects.h

 // Copyright 2015 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_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 #include <memory>
 
@@ skipping 8705 matching lines @@
 
   static void PostGarbageCollectionProcessing(Isolate* isolate);
   static int ArchiveSpacePerThread();
   static char* ArchiveState(Isolate* isolate, char* to);
   static char* RestoreState(Isolate* isolate, char* from);
   static void Iterate(Isolate* isolate, RootVisitor* v);
   static void Iterate(RootVisitor* v, Relocatable* top);
   static char* Iterate(RootVisitor* v, char* t);
 
  private:
+  friend class HeapPointerZapper;  // For |prev_|.
   Isolate* isolate_;
   Relocatable* prev_;
 };
 
 
 // A flat string reader provides random access to the contents of a
 // string independent of the character width of the string.  The handle
 // must be valid as long as the reader is being used.
 class FlatStringReader : public Relocatable {
  public:
   FlatStringReader(Isolate* isolate, Handle<String> str);
   FlatStringReader(Isolate* isolate, Vector<const char> input);
-  void PostGarbageCollection();
+  void PostGarbageCollection() override;
   inline uc32 Get(int index);
   template <typename Char>
   inline Char Get(int index);
   int length() { return length_; }
  private:
   String** str_;
   bool is_one_byte_;
   int length_;
   const void* start_;
 };
@@ skipping 1487 matching lines @@
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #include "src/objects/object-macros-undef.h"
 
 #endif  // V8_OBJECTS_H_