Re-enable an UNREACHABLE in JSObject::GetHeaderSize()

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index e5e8235c292a15049f7afffd4ca0d0b9b9eb85fb..be0cb47dbce51875a548461b250242216a6dd2ed 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -1979,9 +1979,7 @@ int JSObject::GetHeaderSize() {
     case JS_MESSAGE_OBJECT_TYPE:
       return JSMessageObject::kSize;
     default:
-      // TODO(jkummerow): Re-enable this. Blink currently hits this
-      // from its CustomElementConstructorBuilder.
-      // UNREACHABLE();
+      UNREACHABLE();
       return 0;
   }
 }