Debugging help for issue #8734824: WATCHDOG KILLING SYSTEM PROCESS

IActivityController has a new callback which the Watchdog calls
when it detects that the system process is hung.  This may be
use full monkey.  All hail the monkey!

Also add a new private feature to Binder to be able to turn off
all incoming dump() calls to a process.  The watchdog uses this
when it reports it is hung, so that if someone, say, wants to
collect a bug report at this point they won't get stuck waiting
for things that are all busted.

Change-Id: Ib514d97451cf3b93f29e194c1954e29f948c13b1