Add a perf test for async wait and fix a bug in mojo::RunLoop.

mojo/public/c/system/tests/perftest_utils.h

 // Copyright 2016 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.
-//
-// Note: This header should be compilable as C.
 
 #ifndef MOJO_PUBLIC_C_SYSTEM_TESTS_PERFTEST_UTILS_H_
 #define MOJO_PUBLIC_C_SYSTEM_TESTS_PERFTEST_UTILS_H_
 
 #include <functional>
 
 #include "mojo/public/c/system/time.h"
 
 namespace mojo {
 namespace test {
 
 // How long to run each perf test for (in microseconds).
 constexpr MojoTimeTicks kPerftestTimeMicroseconds = 3 * 1000000;
 
 // Iterates the given function for |kPerftestTimeMicroseconds| and reports the
 // number of iterations executed per second.
 void IterateAndReportPerf(const char* test_name,
                           const char* sub_test_name,
                           std::function<void()> single_iteration);
 
 // Sleeps for the given amount of time (in microseconds).
 void Sleep(MojoTimeTicks microseconds);
 
 }  // namespace test
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_C_SYSTEM_TESTS_PERFTEST_UTILS_H_