This made sense when Chromium's //c/b/resources/tools/rollup_plugin.js considered that source JS files could come from both the sources and the generated directories, but this is no longer the case as all those JS files are under <root_gen_dir>/ui/webui/resources/webui_preprocessed now, so we need to update Brave's code to adapt to this new scenario. Chromium change: https://chromium.googlesource.com/chromium/src/+/efc282784459e1ec69a524d901d8694cce5230c5 commit efc282784459e1ec69a524d901d8694cce5230c5 Author: rbpotter <rbpotter@chromium.org> Date: Tue Sep 1 04:37:15 2020 +0000 Web UI: Add preprocessed resources and use in rollup Preprocess all shared JS module resources into: <root_gen_dir>/ui/webui/resources/webui_preprocessed and read all these resources from this directory when bundling with rollup. Bug: 1071641