Add some perftests for wait sets.

mojo/public/c/system/tests/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("../../../mojo_sdk.gni")
 
 mojo_sdk_source_set("tests") {
   testonly = true
 
   mojo_sdk_visibility =
@@ skipping 47 matching lines @@
 }
 
 mojo_sdk_source_set("perftests") {
   testonly = true
 
   sources = [
     "message_pipe_perftest.cc",
     "perftest_utils.cc",
     "perftest_utils.h",
     "reference_perftest.cc",
+    "wait_set_perftest.cc",
   ]
 
   deps = [
     "//testing/gtest",
   ]
 
   mojo_sdk_deps = [
     "mojo/public/c/environment",
     "mojo/public/cpp/system",
     "mojo/public/cpp/test_support",
   ]
 }