Use Mojo pipes to signal sync IPC events

mojo/public/cpp/system/event.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.
+
+#include "mojo/public/cpp/system/event.h"
+
+namespace mojo {
+
+Event::Event() {
+  mojo::MessagePipe pipe;
+  signal_handle_ = std::move(pipe.handle0);
+  wait_handle_ = std::move(pipe.handle1);
+}
+
+Event::~Event() {}
+
+void Event::Signal() {
+  MojoResult rv = mojo::WriteMessageRaw(signal_handle_.get(), nullptr, 0,
+                                        nullptr, 0,
+                                        MOJO_WRITE_MESSAGE_FLAG_NONE);
+  DCHECK_EQ(rv, MOJO_RESULT_OK);
+}
+
+void Event::Reset() {
+  MojoResult rv = MOJO_RESULT_OK;
+  while (rv == MOJO_RESULT_OK) {
+    rv = mojo::ReadMessageRaw(wait_handle_.get(), nullptr, nullptr, nullptr,
+                              nullptr, MOJO_READ_MESSAGE_FLAG_NONE);
+  }
+  DCHECK_EQ(rv, MOJO_RESULT_SHOULD_WAIT);
+}
+
+}  // namespace mojo