It's unfortunate but some of the fields we cleared in I34451000 are accessed
in BG threads or after the activity is destroyed. We could add != null checks
everywhere, but it'll be a mess. I also think it's safer to simply remove
the "= null" lines.
On the other hand, clearing AsyncTasks are relatively safer because they are
kept only so that we can cancel them afterwards, so I kept them. But let me
know if you want to revert the original CL.
Bug 2570603
Change-Id: I04a10dd7382bfcceb686c3e9af92f8949caf619e
78e06eb894