Fix a check failure in the CC background transition.

If there's a process state update from jank perceptible to jank
in-perceptible and a reverse update right after it, there's a chance
that the heap task daemon sees desired_collector_type ==
kCollectorTypeCC rather than kCollectorTypeCCBackground in
DoPendingCollectorTransition() which leads to a !kUseReadBarrier check
failure in TransitionCollector(). The fix is to move this check after
the early return case where collector_type == collector_type_ in
TransitionCollector() like the CMS/Hspace case.

Bug: 31039431
Bug: 12687968
Test: test-art-host, aosp boot with CC, master boot with CC.

Change-Id: I5fe34cb41eaa01c6d8bf80a185253fde6778e852