After the component in bug 634139 is complete, we need to cache representative favicon colors in the places database so they can be quickly displayed in the awesomebar results without repeatedly analyzing each favicon. Whenever favicon data is set on an image that is small enough that it will need to show a colored border in the results, we should analyze the favicon and update the cached representative color. Where this color should sit in the database depends on how bug 751712 turns out.