Add support for enabling DCHECKs in release mode

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 96e044596d29a67bc71aa4c746a44b0c2180f1ac..2b54d71d24afa422c4b915640c65fc22fc00f734 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -1037,9 +1037,9 @@ class Isolate {
   void LinkDeferredHandles(DeferredHandles* deferred_handles);
   void UnlinkDeferredHandles(DeferredHandles* deferred_handles);
 
-#ifdef DEBUG
+#if DCHECK_IS_ON
   bool IsDeferredHandle(Object** location);
-#endif  // DEBUG
+#endif  // DCHECK_IS_ON
 
   bool concurrent_recompilation_enabled() {
     // Thread is only available with flag enabled.
@@ -1179,7 +1179,7 @@ class Isolate {
   // A global counter for all generated Isolates, might overflow.
   static base::Atomic32 isolate_counter_;
 
-#if DEBUG
+#if DCHECK_IS_ON
   static base::Atomic32 isolate_key_created_;
 #endif
 
@@ -1303,7 +1303,7 @@ class Isolate {
   ISOLATE_INIT_ARRAY_LIST(GLOBAL_ARRAY_BACKING_STORE)
 #undef GLOBAL_ARRAY_BACKING_STORE
 
-#ifdef DEBUG
+#if DCHECK_IS_ON
   // This class is huge and has a number of fields controlled by
   // preprocessor defines. Make sure the offsets of these fields agree
   // between compilation units.
@@ -1400,7 +1400,7 @@ class SaveContext BASE_EMBEDDED {
 
 
 class AssertNoContextChange BASE_EMBEDDED {
-#ifdef DEBUG
+#if DCHECK_IS_ON
  public:
   explicit AssertNoContextChange(Isolate* isolate)
     : isolate_(isolate),