Put zapping of local handles behind the extra checks flag.

src/handles.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 142 matching lines @@
 
   inline void CloseScope();
 
   Isolate* isolate_;
   Object** prev_next_;
   Object** prev_limit_;
 
   // Extend the handle scope making room for more handles.
   static internal::Object** Extend(Isolate* isolate);
 
+#ifdef ENABLE_EXTRA_CHECKS
   // Zaps the handles in the half-open interval [start, end).
   static void ZapRange(internal::Object** start, internal::Object** end);
+#endif
 
+  friend class v8::HandleScope;
   friend class v8::internal::DeferredHandles;
-  friend class v8::HandleScope;
   friend class v8::internal::HandleScopeImplementer;
-  friend class v8::ImplementationUtilities;
   friend class v8::internal::Isolate;
 };
 
 
 class DeferredHandles;
 
 
 class DeferredHandleScope {
  public:
   explicit DeferredHandleScope(Isolate* isolate);
@@ skipping 170 matching lines @@
   inline ~HandleDereferenceGuard();
  private:
   Isolate* isolate_;
   bool old_state_;
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_HANDLES_H_