Revert IPC SyncChannel to base::WaitableEvent waiting

ipc/ipc_sync_message_filter.h

 // Copyright (c) 2012 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_IPC_SYNC_MESSAGE_FILTER_H_
 #define IPC_IPC_SYNC_MESSAGE_FILTER_H_
 
 #include <set>
-#include <vector>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/memory/scoped_vector.h"
 #include "base/synchronization/lock.h"
-#include "base/synchronization/waitable_event_watcher.h"
 #include "ipc/ipc_sender.h"
 #include "ipc/ipc_sync_message.h"
 #include "ipc/message_filter.h"
-#include "ipc/mojo_event.h"
 
 namespace base {
 class SingleThreadTaskRunner;
 class WaitableEvent;
 }
 
 namespace IPC {
 class SyncChannel;
 
 // This MessageFilter allows sending synchronous IPC messages from a thread
@@ skipping 22 matching lines @@
   friend class SyncChannel;
 
   void set_is_channel_send_thread_safe(bool is_channel_send_thread_safe) {
     is_channel_send_thread_safe_ = is_channel_send_thread_safe;
   }
 
   void SendOnIOThread(Message* message);
   // Signal all the pending sends as done, used in an error condition.
   void SignalAllEvents();
 
-  void OnShutdownEventSignaled(base::WaitableEvent* event);
-
   // The channel to which this filter was added.
   Sender* sender_;
 
   // Indicates if |sender_|'s Send method is thread-safe.
   bool is_channel_send_thread_safe_;
 
   // The process's main thread.
   scoped_refptr<base::SingleThreadTaskRunner> listener_task_runner_;
 
   // The message loop where the Channel lives.
   scoped_refptr<base::SingleThreadTaskRunner> io_task_runner_;
 
   typedef std::set<PendingSyncMsg*> PendingSyncMessages;
   PendingSyncMessages pending_sync_messages_;
 
   // Messages waiting to be delivered after IO initialization.
-  std::vector<std::unique_ptr<Message>> pending_messages_;
+  ScopedVector<Message> pending_messages_;
 
   // Locks data members above.
   base::Lock lock_;
 
-  base::WaitableEvent* const shutdown_event_;
-
-  // Used to asynchronously watch |shutdown_event_| on the IO thread and forward
-  // to |shutdown_mojo_event_| (see below.)
-  base::WaitableEventWatcher shutdown_watcher_;
-
-  // A Mojo event which can be watched for shutdown. Signals are forwarded to
-  // this event asynchronously from |shutdown_event_|.
-  MojoEvent shutdown_mojo_event_;
+  base::WaitableEvent* shutdown_event_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncMessageFilter);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_SYNC_MESSAGE_FILTER_H_