As in topic. API currently offers fixed ratio only for Mac but not for Windows
shell/browser/ui/views/frameless_view.cc
if (frame_->IsFullscreen())
    return HTCLIENT;
  
  for (auto* view : window_->browser_views()) {
    auto* native_view = static_cast<NativeBrowserViewViews*>(view);
    auto* view_draggable_region = native_view->draggable_region();
    if (view_draggable_region &&
        view_draggable_region->contains(cursor.x(), cursor.y()))
      return HTCAPTION;
  }
  
  
  SkRegion* draggable_region = window_->draggable_region();
  if (draggable_region && draggable_region->contains(cursor.x(), cursor.y()))
    return HTCAPTION;
  
  int frame_component = ResizingBorderHitTest(cursor);
  if (frame_component != HTNOWHERE)
    return frame_component;
  return HTCLIENT;
}
void FramelessView::GetWindowMask(const gfx::Size& size, SkPath* window_mask) {}