Defer expensive UI updates in filmstrip

Bug: 7322925
When using the filmstrip, delay expensive updates to
the action bar and share menus, some of which may require
disk accesses, until the rate of change of photos slows
down, instead of doing this work for every single image
that flies by.

Change-Id: Ie82adb4d54c96fec837d5954a91e1d4a17f548dd