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/util/evsel.c b/tools/perf/util/evsel.c
index fc4faaa..1fb636c 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -519,14 +519,14 @@
 	 * Disabling only independent events or group leaders,
 	 * keeping group members enabled.
 	 */
-	if (!evsel->leader)
+	if (!perf_evsel__is_group_member(evsel))
 		attr->disabled = 1;
 
 	/*
 	 * Setting enable_on_exec for independent events and
 	 * group leaders for traced executed by perf.
 	 */
-	if (perf_target__none(&opts->target) && (!evsel->leader))
+	if (perf_target__none(&opts->target) && !perf_evsel__is_group_member(evsel))
 		attr->enable_on_exec = 1;
 }
 
@@ -707,7 +707,7 @@
 	struct perf_evsel *leader = evsel->leader;
 	int fd;
 
-	if (!leader)
+	if (!perf_evsel__is_group_member(evsel))
 		return -1;
 
 	/*