Cherry pick IndexListAdapter fix into i-dev

ag/1813291 already fixes the bug. Cherry pick it back to i-dev.

Test: Manually verified position of pinned header following
bug repro steps.
Also verified correct behavior when rotating while the header is
fading away.

Bug: 36638590
Change-Id: Ic3c3e97cb6768e96a10c9a36113716090720357a