Bug 977056 - [Dialer] Visual discrepancies: Call ended view under conference call participants list

Yeah, the point is that if you search in Gaia you'll realise that the information (the element attributes) seems to be duplicated. For example, in the SMS app (not to take one of ours but the rest of the cases are just the same):
  1. https://github.com/mozilla-b2g/gaia/blob/master/apps/sms/index.html#L561
  2. https://github.com/mozilla-b2g/gaia/blob/35e87ac4324f0f3abd93dcc70d61c9f37256a0f5/shared/elements/sim_picker.html#L4
On the other hand, personally I prefer the proposed alternative (which BTW is also widely used in most of the <elements> I have found in Gaia (see the Calendar app for example https://github.com/mozilla-b2g/gaia/tree/master/apps/calendar/elements)). It seems to me that having the extends attribute (see https://github.com/mozilla-b2g/gaia/blob/35e87ac4324f0f3abd93dcc70d61c9f37256a0f5/shared/elements/sim_picker.html#L1 but also https://github.com/mozilla-b2g/gaia/blob/master/apps/sms/index.html#L561, this is a form element) would be more than enough to know that this template is for a form element and consequently https://github.com/mozilla-b2g/gaia/blob/35e87ac4324f0f3abd93dcc70d61c9f37256a0f5/shared/elements/sim_picker.html#L4 seems kind of redundant to me.
Last but not least (in fact, probably as the main reason :) ), according to the code in charge of this loading (https://github.com/mozilla-b2g/gaia/blob/master/shared/js/html_imports.js#L14) it seems the right approach is the one proposed, this is not to duplicate the HTML element whose contents are being loaded from the template.
Taking into consideration all this, I would suggest keeping the proposed alternative but please tell me if you prefer otherwise ;) Thanks!