Micro-optimize not-found for elements on objects with empty_fixed_array backing store

BUG=chromium:495949
LOG=n

Review URL: https://codereview.chromium.org/1163033004

Cr-Commit-Position: refs/heads/master@{#28831}

src/lookup-inl.h

@@ -66,6 +66,10 @@ LookupIterator::State LookupIterator::LookupInHolder(Map* const map,
                                               PropertyCellType::kNoCell);
         } else {
           JSObject* js_object = JSObject::cast(holder);
+          if (js_object->elements() == isolate()->heap()->empty_fixed_array()) {
+            return NOT_FOUND;
+          }
+
           ElementsAccessor* accessor = js_object->GetElementsAccessor();
           FixedArrayBase* backing_store = js_object->elements();
           number_ = accessor->GetIndexForKey(backing_store, index_);