perf ui browser: Add method to draw up/down arrow line

It figures out the direction and draws downwards arrows too if that is
the case.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
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-tg329nr7q4dg9d0tl3o0wywg@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>