Add support for enabling DCHECKs in release mode

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index d3e58e8a000da26a8c20b52cd1b54a3582db701c..b53f986233af257fc3d894c9f1586bd75ad6f737 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -1068,7 +1068,7 @@ bool String::MakeExternal(v8::String::ExternalStringResource* resource) {
                   resource->data(),
                   resource->length() * sizeof(smart_chars[0])) == 0);
   }
-#endif  // DEBUG
+#endif                      // ENABLE_SLOW_DCHECKS
   int size = this->Size();  // Byte size of the original string.
   // Abort if size does not allow in-place conversion.
   if (size < ExternalString::kShortSize) return false;
@@ -1135,7 +1135,7 @@ bool String::MakeExternal(v8::String::ExternalOneByteStringResource* resource) {
                   resource->data(),
                   resource->length() * sizeof(smart_chars[0])) == 0);
   }
-#endif  // DEBUG
+#endif                      // ENABLE_SLOW_DCHECKS
   int size = this->Size();  // Byte size of the original string.
   // Abort if size does not allow in-place conversion.
   if (size < ExternalString::kShortSize) return false;
@@ -12016,7 +12016,7 @@ Handle<Map> Map::TransitionToPrototype(Handle<Map> map,
 MaybeHandle<Object> JSObject::SetPrototype(Handle<JSObject> object,
                                            Handle<Object> value,
                                            bool from_javascript) {
-#ifdef DEBUG
+#if DCHECK_IS_ON
   int size = object->Size();
 #endif