base

Change the "start deferred" fragment API to "user visible hint"

Allow a fragment to set a hint of whether or not it is currently user
visible. This will be used implicitly to defer the start of fragments
that are not user visible until the loaders for visible fragments have
run. This hint defaults to true.

Change-Id: Id1349d319886a277ef07301f64f7b9e12c8729bf