DropdownButton doesn't animate newly selected value

[Hixie]

Consider:
https://material-design.storage.googleapis.com/publish/material_v_8/material_ext_publish/0B3321sZLoP_HTS1LdnhrTl9TRzg/components-buttons-otherbuttons-060203_MobileDropdowns_xhdpi_006.webm

When you pick something that isn't the current entry, we should apparently animate the text up a little.

[abarth]

Yeah, I'm not sure if that's a bug in the video or fit that's actually desired. We should follow up with the designers to see what they intended. /cc @sethladd

[sethladd]

I've reached out to the material team for confirmation. Thanks for noticing this behavior!

[sethladd]

The material team responded: "It's a nice to have for the menu, but it's not a high priority."

I think we can punt on this one for our v1 of material.

Thanks for opening the issue to double check. If we decide to implement this, we can reopen.

[Hixie]

Let's keep it open, this would be easy to do and if it's nice to have we should have it. :-)
Doesn't have to block gallery launch though.