Execute pending transactions after FM state change.

Bug 37255517

Because we no longer allow reentrant transactions
during fragment manager state changes, we must
have the pending transactions execute as soon as
the state changes. This allows developers to avoid
calling executePendingTransactions() in lifecycle
calls.

Support Lib: Icdecc018c7cb02f69a694b52c711ba9056469aa5
Test: I269c4c26224c9142d3800a30054f9ddd5b456edb

Change-Id: I849dde6482465e633df33243d99710ebf538cc9a