Comment 7 for bug 1363015

I think you just described how to fix the bug. :-) If the "icon of a particular app comes from its .desktop file from its installation folder", then the way Ubuntu should tell whether it should shape an arbitrary icon is by checking to see if it is one of the icons listed in the .desktop file in its installation folder. If Ubuntu can do that, then an app developer (or Ubuntu contributor) won't need to remember to use an AppIcon component or anything else.