Add heap task processor

The heap task processor processes async tasks which may be delayed.
The motivation for this change is preventing deadlocks which
can occur when the daemon threads get suspended by GetThreadStack.

Other improvements, reduces daemon thread count by one.
Cleaner pending transition VS heap trimming logic.

Bug: 18739541

Change-Id: Idab52b2d9661a6385cada74b93ff297ddc55fc78
Merge "Add heap task processor"