Bug 1098168 - BaseIcon

I think the logic comes from https://github.com/mozilla-b2g/gaia/blob/master/apps/system/js/statusbar.js#L1250

Not sure what's the problem you are mentioning; in observe method of base module, the value of this._settings will be updated each time the {value} of certain {key} is updated and then call _observe_{key}. So there will not be inconsistent cached value, is this what you worry about?