Add support for enabling DCHECKs in release mode

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index bb9ecee0172d71b6348f4e90ed0ee3c7bc5e5850..5e4831b3bc8f781fd8115ffd446787446555379f 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -2147,7 +2147,7 @@ class JSObject: public JSReceiver {
 
   void PrintInstanceMigration(FILE* file, Map* original_map, Map* new_map);
 
-#ifdef DEBUG
+#if DCHECK_IS_ON
   // Structure for collecting spill information about JSObjects.
   class SpillInformation {
    public:
@@ -3071,7 +3071,7 @@ class DescriptorArray: public FixedArray {
   void PrintDescriptors(std::ostream& os);  // NOLINT
 #endif
 
-#ifdef DEBUG
+#if DCHECK_IS_ON
   // Is the descriptor array sorted and without duplicates?
   bool IsSortedNoDuplicates(int valid_descriptors = -1);
 
@@ -8581,7 +8581,7 @@ class StringShape BASE_EMBEDDED {
   inline uint32_t encoding_tag();
   inline uint32_t full_representation_tag();
   inline uint32_t size_tag();
-#ifdef DEBUG
+#if DCHECK_IS_ON
   inline uint32_t type() { return type_; }
   inline void invalidate() { valid_ = false; }
   inline bool valid() { return valid_; }
@@ -8591,7 +8591,7 @@ class StringShape BASE_EMBEDDED {
 
  private:
   uint32_t type_;
-#ifdef DEBUG
+#if DCHECK_IS_ON
   inline void set_valid() { valid_ = true; }
   bool valid_;
 #else