cakephp/debug_kit — comment on commit 56870e2c2f17dcd4bfd42648c1efdfeebd416742
File: Controller/Component/ToolbarComponent.php line 755
By ceeram:

That was the first thing that came on my mind as well, but dogmatic69 said that would cause issues with files manually include()'d and friends. Now that i think of it you can in fact include() any file on the filesystem, and also might not be part of the cakephp application itself too, so i think we should treat files included from not loaded plugins the same. I suggest we go with CakePlugin::loaded() as manually including files is more edge case then not loading all plugins