Ensure AdapterView doesn't post selection notifications forever

Previously we would loop forever if a selection notification was
posted after data had changed but the data changed bit was never
reset (e.g. a layout pass never occurred). This moves the pending
notification to occur as part of a layoutChildren() /
checkSelectionChanged() pass. If the client does horrible things
to prevent layout, no notification will occur -- but we won't loop
forever.

BUG: 17736536
Change-Id: I9773a769ad402c92dcbe2af7b8982d4443001961