Add support for enabling DCHECKs in release mode

src/api.cc

 // 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.
 
 #include "src/api.h"
 
 #include <string.h>  // For memcpy, strlen.
 #ifdef V8_USE_ADDRESS_SANITIZER
 #include <sanitizer/asan_interface.h>
 #endif  // V8_USE_ADDRESS_SANITIZER
@@ skipping 7549 matching lines @@
 
 
 char* HandleScopeImplementer::RestoreThread(char* storage) {
   MemCopy(this, storage, sizeof(*this));
   *isolate_->handle_scope_data() = handle_scope_data_;
   return storage + ArchiveSpacePerThread();
 }
 
 
 void HandleScopeImplementer::IterateThis(ObjectVisitor* v) {
-#ifdef DEBUG
+#if DCHECK_IS_ON
   bool found_block_before_deferred = false;
 #endif
   // Iterate over all handles in the blocks except for the last.
   for (int i = blocks()->length() - 2; i >= 0; --i) {
     Object** block = blocks()->at(i);
     if (last_handle_before_deferred_block_ != NULL &&
         (last_handle_before_deferred_block_ <= &block[kHandleBlockSize]) &&
         (last_handle_before_deferred_block_ >= block)) {
       v->VisitPointers(block, last_handle_before_deferred_block_);
       DCHECK(!found_block_before_deferred);
-#ifdef DEBUG
+#if DCHECK_IS_ON
       found_block_before_deferred = true;
 #endif
     } else {
       v->VisitPointers(block, &block[kHandleBlockSize]);
     }
   }
 
   DCHECK(last_handle_before_deferred_block_ == NULL ||
          found_block_before_deferred);
 
@@ skipping 105 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);
   callback(info);
 }
 
 
 } }  // namespace v8::internal