Fix a CC 145-alloc-tracking-stress deadlock.

When the allocation tracking gets disabled, there may be threads
blocking on the system weak access for recording allocations, but when
GC reenables the system weak access, it fails to wake up those blocked
threads (which causes a deadlock) because the broadcast call is guarded
by Heap::IsAllocTrackingEnabled(), which is false at this point.

Broadcast in Heap::BroadcastForNewAllocationRecords() regardless of
Heap::IsAllocTrackingEnabled(), which is safe.

Also apply a similar fix for the non-CC case.

Bug: 27467554
Change-Id: I74cf88bceb306589ce11a19a688be223e099e88a