This allows passing a timer to be run periodically, which will update
the hists tree that then gers refreshed on the screen, just like the
Live mode (symbol entries, annotation) we already have in 'perf top
--tui'.

Will be used by the new hist_entry/hists based 'top' tool.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-2r44qd8oe4sagzcgoikl8qzc@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>