perf evsel: Introduce is_group_member method

To clarify what is being tested, instead of assuming that evsel->leader
== NULL means either an 'isolated' evsel or a 'group leader'.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.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-lvdbvimaxw9nc5een5vmem0c@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 557081e..c247fac 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -152,7 +152,8 @@
 		return 0;
 	}
 
-	if (!perf_target__has_task(&target) && (!evsel->leader)) {
+	if (!perf_target__has_task(&target) &&
+	    !perf_evsel__is_group_member(evsel)) {
 		attr->disabled = 1;
 		attr->enable_on_exec = 1;
 	}