Add IPC::ForwardingMessageFilter.

ipc/ipc_forwarding_message_filter.h

Index: ipc/ipc_forwarding_message_filter.h
diff --git a/ipc/ipc_forwarding_message_filter.h b/ipc/ipc_forwarding_message_filter.h
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+// 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_FORWARDING_MESSAGE_FILTER_H_
+#define IPC_IPC_FORWARDING_MESSAGE_FILTER_H_
+
+#include <set>
+
+#include "base/bind.h"
+#include "base/callback_forward.h"
+#include "base/synchronization/lock.h"
+#include "base/task_runner.h"
+#include "ipc/ipc_channel_proxy.h"
+
+namespace IPC {
+
+// This class can be used to intercept routed messages and
+// deliver them to a different task runner than they would otherwise
+// be sent. Messages are filtered based on
+// based on routing_id as well as type (see message_ids_to_filter and AddRoute
+// and RemoveRoute).
+//
+// The user of this class implements ForwardingMessageFilter::Client,
+// which will receive the intercepted messages, on the specified target thread.
+class IPC_EXPORT ForwardingMessageFilter : public ChannelProxy::MessageFilter {
+ public:
+
+  // The handler is invoked on the thread associated with
+  // |target_task_runner| with messages that were intercepted by this filter.
+  typedef base::Callback<void(const Message&)> Handler;
+
+  // This filter will intercept |message_ids_to_filter| and post
+  // them to the provided |target_task_runner|, where they will be given
+  // to |handler|.
+  //
+  // The caller must ensure that |handler| outlives the lifetime of the filter.
+  ForwardingMessageFilter(
+      const uint32* message_ids_to_filter,
+      size_t num_message_ids_to_filter,
+      base::TaskRunner* target_task_runner,
+      const Handler& handler);
+
+  // Define the message routes to be filtered.
+  void AddRoute(int routing_id);
+  void RemoveRoute(int routing_id);
+
+  // ChannelProxy::MessageFilter methods:
+  virtual bool OnMessageReceived(const Message& message) OVERRIDE;
+
+ private:
+  friend class ChannelProxy::MessageFilter;
+  virtual ~ForwardingMessageFilter();
+
+  void ForwardToHandler(const Message& message);
+
+  std::set<int> message_ids_to_filter_;
+
+  // The handler_ only gets Run on the thread corresponding to
+  // target_task_runner_.
+  scoped_refptr<base::TaskRunner> target_task_runner_;
+  Handler handler_;
+
+  // Protects access to routes_.
+  base::Lock routes_lock_;
+
+  // Indicates the routing_ids for which messages should be filtered.
+  std::set<int> routes_;
+
+  DISALLOW_COPY_AND_ASSIGN(ForwardingMessageFilter);
+};
+
+}  // namespace IPC
+
+#endif  // IPC_IPC_FORWARDING_MESSAGE_FILTER_H_