Add support for enabling DCHECKs in release mode

src/contexts.h

 // 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.
 
 #ifndef V8_CONTEXTS_H_
 #define V8_CONTEXTS_H_
 
 #include "src/heap/heap.h"
 #include "src/objects.h"
 
@@ skipping 583 matching lines @@
 
   typedef FixedBodyDescriptor<
       kHeaderSize,
       kHeaderSize + FIRST_WEAK_SLOT * kPointerSize,
       kSize> MarkCompactBodyDescriptor;
 
  private:
   // Unchecked access to the slots.
   Object* unchecked_previous() { return get(PREVIOUS_INDEX); }
 
-#ifdef DEBUG
+#if DCHECK_IS_ON
   // Bootstrapping-aware type checks.
   static bool IsBootstrappingOrValidParentContext(Object* object, Context* kid);
   static bool IsBootstrappingOrGlobalObject(Isolate* isolate, Object* object);
 #endif
 
   STATIC_ASSERT(kHeaderSize == Internals::kContextHeaderSize);
   STATIC_ASSERT(EMBEDDER_DATA_INDEX == Internals::kContextEmbedderDataIndex);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_CONTEXTS_H_