Attached is a trace for starting up the keyboard-shortcut-viewer. Look specifically at the 'Service: shortcut_viewer_app' process. The initial views::Widget set up (in Widget::Init()) takes ~490ms, and the following first paint takes ~25ms, followed by another ~50ms of raster. Some interesting observations:
 . RenderTextHarfBuzz:EnsureLayoutRunList() gets called ~3000 times during Widget::Init().
 . View::Layout(bounds_changed) gets called ~2400 times.
 . RenderTextHarfBuzz:EnsureLayoutRunList() is called twice before Widget::Init(), each of which takes 20+ms (I assume during KeyboardShortcutView::InitViews()).

This seems unnaturally expensive. We should probably look into optimizing the views layout code. I am not familiar with RenderTextHarfBuzz or other parts of text-layout code, but perhaps something could be improved there too?

cc'ing some chromeos UI folks, other people who are working on related issues (e.g.  issue 835983 , issue 858944 etc.)
 

Deleted: trace_ksv-create.json.gz 866 KB

trace_ksv-create.json.gz 866 KB Download