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

mojo/public/cpp/environment/tests/run_loop_async_wait_perftest.cc

+// 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.
+
+// This file has perf tests for async waits using |mojo::RunLoop| (i.e., the
+// "standalone" |Environment|).
+
+#include <stdio.h>
+
+#include "mojo/public/c/environment/tests/async_waiter_perftest_helpers.h"
+#include "mojo/public/cpp/environment/environment.h"
+#include "mojo/public/cpp/test_support/test_support.h"
+#include "mojo/public/cpp/utility/run_loop.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace mojo {
+namespace {
+
+constexpr MojoTimeTicks kPerftestTimeMicroseconds = 3 * 1000000;
+
+TEST(RunLoopAsyncWaitPerftest, SingleThreaded) {
+  for (uint32_t num_handles = 1u; num_handles <= 10000u; num_handles *= 10u) {
+    RunLoop run_loop;
+
+    MojoTimeTicks start_time = 0;
+    MojoTimeTicks end_time = 0;
+    uint64_t raw_result = test::DoAsyncWaiterPerfTest(
+        Environment::GetDefaultAsyncWaiter(), num_handles,
+        [&start_time, &end_time]() {
+          RunLoop::current()->PostDelayedTask(
+              []() { RunLoop::current()->Quit(); }, kPerftestTimeMicroseconds);
+          start_time = MojoGetTimeTicksNow();
+          RunLoop::current()->Run();
+          end_time = MojoGetTimeTicksNow();
+        });
+
+    double result = static_cast<double>(raw_result) /
+                    (static_cast<double>(end_time - start_time) / 1000000.0);
+    char sub_test_name[100] = {};
+    sprintf(sub_test_name, "%u", static_cast<unsigned>(num_handles));
+    test::LogPerfResult("RunLoopAsyncWaitPerftest.SingleThreaded",
+                        sub_test_name, result, "callbacks/second");
+  }
+}
+
+}  // namespace
+}  // namespace mojo