Add thunks for wait set operations, together with public tests.

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 =
       [ "mojo/public/cpp/system/tests:mojo_public_system_unittests" ]
 
   cflags_c = [ "-Wundef" ]
 
   sources = [
     "buffer_unittest.cc",
     "compile_unittest.cc",
     "data_pipe_unittest.cc",
     "handle_unittest.cc",
     "macros_unittest.cc",
     "message_pipe_unittest.cc",
     "result_unittest.cc",
     "time_unittest.cc",
+    "wait_set_unittest.cc",
     "wait_unittest.cc",
   ]
 
   deps = [
     ":pure_tests",
     "//testing/gtest",
   ]
 
   mojo_sdk_deps = [
     "mojo/public/c/environment",
@@ skipping 32 matching lines @@
   deps = [
     "//testing/gtest",
   ]
 
   mojo_sdk_deps = [
     "mojo/public/c/environment",
     "mojo/public/cpp/system",
     "mojo/public/cpp/test_support",
   ]
 }