Use WaitableEvents to wake up sync IPC waiting

ipc/mojo_event.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.
-
-#ifndef IPC_MOJO_EVENT_H_
-#define IPC_MOJO_EVENT_H_
-
-#include "base/macros.h"
-#include "base/synchronization/lock.h"
-#include "mojo/public/cpp/system/message_pipe.h"
-
-namespace IPC {
-
-// A MojoEvent is a simple wrapper around a Mojo message pipe which supports
-// common WaitableEvent-like methods of Signal() and Reset(). This class exists
-// to support the transition from legacy IPC to Mojo IPC and is not intended for
-// general use outside of src/ipc. Unlike base::WaitableEvent, all MojoEvents
-// must be manually reset.
-class MojoEvent {
- public:
-  // Constructs a new MojoEvent that is initially not signaled.
-  MojoEvent();
-
-  ~MojoEvent();
-
-  // Gets a Handle that can be waited on for this MojoEvent. When the Event is
-  // signaled, this handle will have |MOJO_HANDLE_SIGNAL_READABLE| satisfied.
-  const mojo::Handle& GetHandle() const { return wait_handle_.get(); }
-
-  void Signal();
-  void Reset();
-
- private:
-  mojo::ScopedMessagePipeHandle signal_handle_;
-  mojo::ScopedMessagePipeHandle wait_handle_;
-
-  base::Lock lock_;
-  bool is_signaled_ = false;
-
-  DISALLOW_COPY_AND_ASSIGN(MojoEvent);
-};
-
-}  // namespace IPC
-
-#endif  // IPC_MOJO_EVENT_H_