Introduce a handle zapping setting, and enable it by default for release and debug

src/api.cc

 // Copyright 2012 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 7961 matching lines @@
 void HandleScopeImplementer::BeginDeferredScope() {
   ASSERT(last_handle_before_deferred_block_ == NULL);
   last_handle_before_deferred_block_ = isolate()->handle_scope_data()->next;
 }
 
 
 DeferredHandles::~DeferredHandles() {
   isolate_->UnlinkDeferredHandles(this);
 
   for (int i = 0; i < blocks_.length(); i++) {
-#ifdef ENABLE_EXTRA_CHECKS
+#ifdef ENABLE_HANDLE_ZAPPING
     HandleScope::ZapRange(blocks_[i], &blocks_[i][kHandleBlockSize]);
 #endif
     isolate_->handle_scope_implementer()->ReturnBlock(blocks_[i]);
   }
 }
 
 
 void DeferredHandles::Iterate(ObjectVisitor* v) {
   ASSERT(!blocks_.is_empty());
 
@@ skipping 53 matching lines @@
   Isolate* isolate = reinterpret_cast<Isolate*>(info.GetIsolate());
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   return callback(info);
 }
 
 
 } }  // namespace v8::internal