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diff --git a/ipc/ipc_sync_message_filter.h b/ipc/ipc_sync_message_filter.h
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+++ b/ipc/ipc_sync_message_filter.h
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+// Copyright (c) 2011 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_
+#pragma once
+
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
+#include "ipc/ipc_channel_proxy.h"
+#include "ipc/ipc_sync_message.h"
+#include <set>
+
+namespace base {
+class WaitableEvent;
+}
+
+class MessageLoop;
+
+namespace IPC {
+
+class MessageReplyDeserializer;
+
+// This MessageFilter allows sending synchronous IPC messages from a thread
+// other than the listener thread associated with the SyncChannel.  It does not
+// support fancy features that SyncChannel does, such as handling recursion or
+// receiving messages while waiting for a response.  Note that this object can
+// be used to send simultaneous synchronous messages from different threads.
+class IPC_EXPORT SyncMessageFilter : public ChannelProxy::MessageFilter,
+                                     public Message::Sender {
+ public:
+  explicit SyncMessageFilter(base::WaitableEvent* shutdown_event);
+  virtual ~SyncMessageFilter();
+
+  // Message::Sender implementation.
+  virtual bool Send(Message* message);
+
+  // ChannelProxy::MessageFilter implementation.
+  virtual void OnFilterAdded(Channel* channel);
+  virtual void OnChannelError();
+  virtual void OnChannelClosing();
+  virtual bool OnMessageReceived(const Message& message);
+
+ private:
+  void SendOnIOThread(Message* message);
+  // Signal all the pending sends as done, used in an error condition.
+  void SignalAllEvents();
+
+  // The channel to which this filter was added.
+  Channel* channel_;
+
+  MessageLoop* listener_loop_;  // The process's main thread.
+  MessageLoop* io_loop_;  // The message loop where the Channel lives.
+
+  typedef std::set<PendingSyncMsg*> PendingSyncMessages;
+  PendingSyncMessages pending_sync_messages_;
+
+  // Locks data members above.
+  base::Lock lock_;
+
+  base::WaitableEvent* shutdown_event_;
+
+  DISALLOW_COPY_AND_ASSIGN(SyncMessageFilter);
+};
+
+}  // namespace IPC
+
+#endif  // IPC_IPC_SYNC_MESSAGE_FILTER_H_