Add support for enabling DCHECKs in release mode

src/handles.cc

Index: src/handles.cc
diff --git a/src/handles.cc b/src/handles.cc
index d9b130f3cac3d0d25dfd8072e347e4e5614fa1e7..055cac429a6860c97334baa24c0fb6df4829d95a 100644
--- a/src/handles.cc
+++ b/src/handles.cc
@@ -98,7 +98,7 @@ DeferredHandleScope::DeferredHandleScope(Isolate* isolate)
   DCHECK(data->limit == &impl_->blocks()->last()[kHandleBlockSize]);
   impl_->blocks()->Add(new_next);
 
-#ifdef DEBUG
+#if DCHECK_IS_ON
   prev_level_ = data->level;
 #endif
   data->level++;
@@ -121,7 +121,7 @@ DeferredHandles* DeferredHandleScope::Detach() {
   HandleScopeData* data = impl_->isolate()->handle_scope_data();
   data->next = prev_next_;
   data->limit = prev_limit_;
-#ifdef DEBUG
+#if DCHECK_IS_ON
   handles_detached_ = true;
 #endif
   return deferred;