perf hist: Introduce routine to measure lenght of formatted entry

Will be used to figure out the window width needed in the new tree
widget.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/hist.h

@@ -141,4 +141,7 @@ int hist_entry__tui_annotate(struct hist_entry *self);
 
 int hists__tui_browse_tree(struct rb_root *self, const char *help);
 #endif
+
+unsigned int hists__sort_list_width(struct hists *self);
+
 #endif	/* __PERF_HIST_H */