Make JSProxies always be in slow mode

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index fea916b03292676f5f088249f161b424ceb22b95..0509a80b2329c74a406e82987304dbafeeee6f59 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -7067,7 +7067,13 @@ MaybeHandle<Object> Object::GetPropertyOrElement(Handle<JSReceiver> holder,
 
 void JSReceiver::initialize_properties() {
   DCHECK(!GetHeap()->InNewSpace(GetHeap()->empty_fixed_array()));
-  WRITE_FIELD(this, kPropertiesOffset, GetHeap()->empty_fixed_array());
+  DCHECK(!GetHeap()->InNewSpace(GetHeap()->empty_properties_dictionary()));
+  if (map()->is_dictionary_map()) {
+    WRITE_FIELD(this, kPropertiesOffset,
+                GetHeap()->empty_properties_dictionary());
+  } else {
+    WRITE_FIELD(this, kPropertiesOffset, GetHeap()->empty_fixed_array());
+  }
 }