perf evlist: Introduce id_hdr_size method out of perf_session

We will need this when not using perf_session in cases like 'perf top'
and strace where no perf.data file is created nor consumed.

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-za923wjc41q5xot5vrhuhj3j@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index a76666f..675e080 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -78,39 +78,12 @@
 	return -1;
 }
 
-static void perf_session__id_header_size(struct perf_session *session)
-{
-       struct perf_sample *data;
-       u64 sample_type = session->sample_type;
-       u16 size = 0;
-
-	if (!session->sample_id_all)
-		goto out;
-
-       if (sample_type & PERF_SAMPLE_TID)
-               size += sizeof(data->tid) * 2;
-
-       if (sample_type & PERF_SAMPLE_TIME)
-               size += sizeof(data->time);
-
-       if (sample_type & PERF_SAMPLE_ID)
-               size += sizeof(data->id);
-
-       if (sample_type & PERF_SAMPLE_STREAM_ID)
-               size += sizeof(data->stream_id);
-
-       if (sample_type & PERF_SAMPLE_CPU)
-               size += sizeof(data->cpu) * 2;
-out:
-       session->id_hdr_size = size;
-}
-
 void perf_session__update_sample_type(struct perf_session *self)
 {
 	self->sample_type = perf_evlist__sample_type(self->evlist);
 	self->sample_size = __perf_evsel__sample_size(self->sample_type);
 	self->sample_id_all = perf_evlist__sample_id_all(self->evlist);
-	perf_session__id_header_size(self);
+	self->id_hdr_size = perf_evlist__id_hdr_size(self->evlist);
 }
 
 int perf_session__create_kernel_maps(struct perf_session *self)