perf tools: Introduce per user view

The new --uid command line option will show only the tasks for a given
user, using the proc interface to figure out the existing tasks.

Kernel work is needed to close races at startup, but this should already
be useful in many use cases.

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-bdnspm000gw2l984a2t53o8z@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index 64f8bee..92af168 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -188,6 +188,7 @@
 struct perf_record_opts {
 	pid_t	     target_pid;
 	pid_t	     target_tid;
+	uid_t	     uid;
 	bool	     call_graph;
 	bool	     group;
 	bool	     inherit_stat;